# Amps ????



## DJMotorhomer (Apr 15, 2010)

Hi All

I am not repeat not a technical man by any means being an ex Naval Chef - give me a recipe and off I go at full throttle. But when it comes to amps, volts etc I am totally lost.

We go to some camps that state 10 amps maximum to be used.

How do I work out what makes 10 amps. We use our Truma combi boiler on electric for heating and hot water and have a normal tv. We have a low voltage toaster and kettle, a normal kettle and a whistling one. How do I work out what amps I am using and what each appliance uses ??? :roll: 

Cheers

DJM


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## bigtwin (May 24, 2008)

I (amps) = W(watts)/V(volts)

So, a 1kW device draws 1000/250v = 4 amps


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## bognormike (May 10, 2005)

not an expert by any means but I work it out as watts divided by voltage = amps. So if you've got an appliance that is rated at 2kw (2000 watts), and the voltage is 200 (well, nominally 220, but say 200 to make it easy!), it's using 10amps.


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## bigcats30 (Aug 13, 2012)

Watts ÷ Volts = Amps

Look on any device an it should tell you what its wattage is/amps then using the simple formula above will let you know how many amps you are using.

You can also read this and it will tell you roughly what ampage a device will use (obviously its a guide and not exact)

 CClub device usage


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## TR5 (Jun 6, 2007)

Most electrical items will have a rating on them, i.e. a 1kw heater would be 1000 watts. (1kw = 1000w)
Divide the wattage by the voltage, and you get amps.

i.e. 1000w (1kw) / 230volts = 4.34 amps.

So a 16amp supply will give you about 3.5kw (3500watts) to play with.
A 10amp supply will give you around 2.3kw (2300watts) to play with.

Watts divided by Volts = Amps
Amps x Volts = Watts......

HTH

Michael


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## davidmac (Jan 15, 2012)

Hi I happened to be looking at the spec of my Truma boiler earlier this week and the electric water heater is rated at 800 watts
Regards David


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## bognormike (May 10, 2005)

my truma has 2 settings, I thought it was 1800 or 900 watts, you can set it at the lower one for "slow" electricity. :lol: 

We were on the aire at Honfleur last month and there must have been about 5 amps, it kept going off when somebody turned their kettle on :roll:


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## Jumbocruiser (Aug 22, 2010)

I made this device:









From one of these AC Clamp Meters:










Basically clamping the meter around the mains inlet to the MH, and having a remote display that can be placed in a location that is easier to access.

Now I always know how much current (amps) we are drawing, and therefor how much spare capacity is available.

By switching on appliances one at a time you can see how much current it draws and next time you are close to the limit you will know if you will get away with turning it on!


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## Patrick_Phillips (Aug 17, 2006)

If your device is marked as 150VA then, as Wikipedia puts it:

_A volt-ampere (VA) is the unit used for the apparent power in an electrical circuit, equal to the product of root-mean-square (RMS) voltage and RMS current.[1] In direct current (DC) circuits, this product is equal to the real power (active power) [2] in watts. Volt-amperes are useful only in the context of alternating current (AC) circuits (sinusoidal voltages and currents of the same frequency)._

But to you and me - it means watts (near enough).

Patrick


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## Penquin (Oct 15, 2007)

A thing to remember is that in the UK nominal voltage is 240 volts whereas in France for example it is 220.

That is perfectly acceptable to all machines since it is always stated as e.g. 230 + or - 10% i.e. within the range 207 to 253 - which if course 240 is......

So it is best to use as near the correct voltage as possible since as said

1000w (kettle) at 240 volts = 1000/240 = 4.17 amps (the extra 0.17 amps all adds up if the supply is limited to say 6 amps)

1000w (same kettle) at 220 volts = 1000/220 = 4.54 amps (more than at the higher voltage).

That is a difference between e.g. UK campsites and French ones......

Current supplies are often more restricted in France or similar whereas in the UK many sites supply 16 amps - more than enough for everything; microwave 600w), heating (say 900 w), toaster (600w). kettle (600w) = 2700 w total (2700 / 240 = 11.25 amps). In France 6 amps maximum is not unusual and on some sites there may be a 3 amp limit...... that can be very taxing to say the least as it negates the chance of using heating nby itself or two of the others at the same time......

Measuring the current being used is not always accurate - neither is the supply limit absolutley precise - in some there may be considerable tolerance, in others virtually none.......

The answer is to be as economic with power as possible and think carefully before switching things on - the start up current for many applicance exceeds the amount normally required by a large measure.....

It also of course depends on how the cut off is managed - if it is a simple current measuring device it may be possible to reset it, if a fuse has blown that may require specialist sorting out - fuses usually have a greater tolerance to overload than trips....... but you can never rely on it......

Good luck and just be sensible - the formulae given will work if used to give you an indication of the current being used but there are often unkown things such as the tripping device accuracy, or even the value it has been determined to be........

Dave


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## listerdiesel (Aug 3, 2012)

The ratings for kW and KVA are not interchangeable, you multiply kVA by a constant called the Power Factor (abb: pf ) to give kW.

This is due to the reactance of things like motors and flourescent ballast chokes that effects how they are 'seen' by the supply.

Power Factor varies from Unity (1) down to a fraction which can be as low as 0.5 or 0.6 for inductive loads.

Thus a resistive load like an electric water heater has a power factor of 1, while a decent size electric induction motor will be down towards 0.6.

In practice, industry uses a figure of 0.8pf for rating generators and the like, but if you've ever tried running a microwave off a small generator, you will know that you need a larger generator rating than is suggested by the microwave rating label. This is a direct result of the low power factor of the microwave.

Peter


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## emmbeedee (Oct 31, 2008)

Penquin said:


> A thing to remember is that in the UK nominal voltage is 240 volts whereas in France for example it is 220.
> 
> That is perfectly acceptable to all machines since it is always stated as e.g. 230 + or - 10% i.e. within the range 207 to 253 - which if course 240 is......
> 
> Dave


(Pedant mode on  )

In the UK electricity is supplied at 230 V +10% - 6% (BS 7671 Appendix 2 section 14, according to Wiki.)

Used to be 240 V +/- 6% but changed to suit the EU. Thus original gave a max. of 254.4 V wheras the new standard gives a max. of 253 V as you stated, insignificant difference really. I presume this gave the EU bureaucrats bragging rights that they'd standardised something without actually achieving anything.
I have measured 253 V at this house & 254 V in a previous house.


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## oldun (Nov 10, 2005)

Resistive devices like electric kettle and fan heaters will have different consumptions at different voltages. The lower the voltage the lower the watts consumed.

However if all is working to plan all of us Europeans should have 230V electricity so this problem should not arise.

However a "240V" kettle in the USA (110V) will take forever to boil the water


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## listerdiesel (Aug 3, 2012)

oldun said:


> However a "240V" kettle in the USA (110V) will take forever to boil the water


Strange to relate, most USA homes have 240V available for high-power consumers like cookers.

Their electricity is distributed at 120-0-120 over two phases, so ground to 1 phase is 120, ground to the other phase is 120 but phase to phase is 240V.

The actual figures vary with the supply, but I'm sure the basic principal will be obvious.

Just been talking with our friend Tim in San Jose about his impending house purchase and move, and looking at what supplies he had to the house.

Peter


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## Scattycat (Mar 29, 2011)

DJMotorhomer said:


> Hi All
> 
> I am not repeat not a technical man by any means being an ex Naval Chef - give me a recipe and off I go at full throttle. But when it comes to amps, volts etc I am totally lost.
> 
> ...


I am also not an expert 'at this MH'ing game', but I don't understand why you need 3 kettles. (?)


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## BillCreer (Jan 23, 2010)

Scattycat said:


> DJMotorhomer said:
> 
> 
> > Hi All
> ...


I don't think there is any harm in having a small collection so long as you don't let it rule your life.


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## Frantone (Sep 6, 2006)

There used to be a device available, Reich Fuse Control, on which you could set the level at which it cut off the supply to your van. i.e. if you knew the available supply was 6 amps then you could set the control to trip out before the supply thus avoiding having to get the campsite staff to reset the bollard/supply. There does not seem to be anything similar currently available, unless somebody knows differently?


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## pippin (Nov 15, 2007)

Mr Naval Chef:

_We have a low voltage toaster and kettle_

That I very much doubt as I assume that by low voltage you mean 12V.

What you almost certainly have is a mains 230V kettle and toaster that are low wattage.
They will probably take ages to boil or brown a slice of toast.

Mr Elephant:

_Basically clamping the meter around the mains inlet to the MH_

Err - no.

You need to clamp the meter around either the neutral wire or the live wire.

If you clamp it around the entire three-core cable you will read nothing.

Just trying to help.


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## drcotts (Feb 23, 2006)

listerdiesel said:


> The ratings for kW and KVA are not interchangeable, you multiply kVA by a constant called the Power Factor (abb: pf ) to give kW.
> 
> This is due to the reactance of things like motors and flourescent ballast chokes that effects how they are 'seen' by the supply.
> 
> ...


Lister is right and if you put one of those domestic power meters in line with an AC pump or similar it will seem like its drawing twice the rated current when in fact its not because as lister says you have to then multiply this by the power factor of say 0.6 to get the real current drawn.


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## soundman (May 1, 2005)

What is the typical/average rating for the mcb in a motorhome consumer unit?
Our's is 10amp but frequently trips at around 8.5 amps.
I am thinking of separating the two circuits and using two mcb's
Any advice?


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## clive1821 (Mar 27, 2010)

Yep it realy depends, i have a 6 way consumer unit in my van some cbs are 6amp and the rest are 10amp but it all is dependant on the supply to your van and indeed what equipment you are using in the van


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## listerdiesel (Aug 3, 2012)

soundman said:


> What is the typical/average rating for the mcb in a motorhome consumer unit?
> Our's is 10amp but frequently trips at around 8.5 amps.
> I am thinking of separating the two circuits and using two mcb's
> Any advice?


Before you start changing anything, look at the 'TYPE' of MCB, they come in four flavours to suit different devices:

A, B, C and D.

A is for purely resistive loads which cause little or no current surge when they are turned on. There is a thermal element to the rating, it will normally trip at 1.5 X full load current immediately, but the thermal element ensures that it does trip at 1.1 X full load rating

B and C are the intermediate ratings, getting from the purely resistive of the 'A' rating up to the purely inductive of the 'D' rating. They include a thermal element and a magnetic element:
Type B trips between 3 and 5 time full load current on startup surge 
Type C trips between 5 and 10 times full load current on startup surge. Both types also trip on a thermal load basis at just over the rated load current, but their surge handling is far greater than the A type.

D Is for largely inductive loads such as transformers and induction motors. Type D trips between 10 and 20 times full load current. We use these on our chargers. They also have thermal tripping.

For m/h use, type A or B should be fine.

You shouldn't need to use anything heavier.

Peter


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## emmbeedee (Oct 31, 2008)

listerdiesel said:


> oldun said:
> 
> 
> > However a "240V" kettle in the USA (110V) will take forever to boil the water
> ...


Peter, when I lived over there I often heard the supply described, (but not by electricians, :?) as "2 phases". An electrical engineer told me this is an incorrect description, as what they actually use is a centre tapped transformer, such that from either end to the centre tapping gives 110 - 120 volts & from end to end gives 220 - 240 volts. 
I was employed in automotive electrical/electronics so have no direct knowledge of their supply system. I do remember that every fourth or fifth pole had a transformer mounted on it, so the main supply must have been at fairly low voltage. Made the local streets look very unattractive too, poles, wires & transformers everywhere. The transformers seemed to blow up quite often too, probably because there were so many of them.
Another strange thing is that although their 110/120 plug is a universal standard, even between 2 & 3 pin versions, there are a plethora of plugs for the 220 volt supply. Some friends of ours bought a new tumble dryer & to their amazement it was delivered without a mains plug. They couldn't get over this, never seen anything like it, etc. as everything over there always comes with a plug fitted!
They insisted the supplier supply & fit a plug & he tried several but none was correct. In the end they sent it back & ordered from another supplier with the proviso that a correct plug must be fitted. I did suggest the obvious of removing the plug off the old one but that had already been disposed of.
Most tumble dryers in the US, at least in our area, were gas so this was a fairly unusual domestic appliance.


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## soundman (May 1, 2005)

clive1821 said:


> Yep it realy depends, i have a 6 way consumer unit in my van some cbs are 6amp and the rest are 10amp but it all is dependant on the supply to your van and indeed what equipment you are using in the van


Our Hymer just has the one 10amp (B) rated mcb which as I say often trips at under 9 amps.
The two circuits comprise of:
1. Truma boiler (dual heat)
2. Control panel and electro block and the 13a sockets plus underfloor heating (400w)
I had thought of splitting the circuits into 2x10A
Soundman


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## listerdiesel (Aug 3, 2012)

emmbeedee said:


> Peter, when I lived over there I often heard the supply described, (but not by electricians, :?) as "2 phases". An electrical engineer told me this is an incorrect description, as what they actually use is a centre tapped transformer, such that from either end to the centre tapping gives 110 - 120 volts & from end to end gives 220 - 240 volts.
> I was employed in automotive electrical/electronics so have no direct knowledge of their supply system. I do remember that every fourth or fifth pole had a transformer mounted on it, so the main supply must have been at fairly low voltage. Made the local streets look very unattractive too, poles, wires & transformers everywhere. The transformers seemed to blow up quite often too, probably because there were so many of them.
> Another strange thing is that although their 110/120 plug is a universal standard, even between 2 & 3 pin versions, there are a plethora of plugs for the 220 volt supply. Some friends of ours bought a new tumble dryer & to their amazement it was delivered without a mains plug. They couldn't get over this, never seen anything like it, etc. as everything over there always comes with a plug fitted!
> They insisted the supplier supply & fit a plug & he tried several but none was correct. In the end they sent it back & ordered from another supplier with the proviso that a correct plug must be fitted. I did suggest the obvious of removing the plug off the old one but that had already been disposed of.
> Most tumble dryers in the US, at least in our area, were gas so this was a fairly unusual domestic appliance.


Yes, technically correct, it is a centre-tapped 240V for most users, but not universally so, and I got into the bad habit of calling it two phases whereas it wasn't always so.

Their 110V plugs and sockets are pretty dire, but they see our 13A plug as over-engineered!

Peter


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## raynipper (Aug 4, 2008)

Just a thought Peter.
I have a 5.5 kva. 240v. to 120v. transformer surplus to requirements.
I used the last one in our Eagle RV that had a 50 amp supply cord.

Can't post it though.

Ray.


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## joedenise (Jul 20, 2007)

Ray - it's a good job you can't post that as it would be advertising :lol: :lol: :lol: 

Joe


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## soundman (May 1, 2005)

listerdiesel said:


> soundman said:
> 
> 
> > What is the typical/average rating for the mcb in a motorhome consumer unit?
> ...


Hi Peter
You quote "Both types also trip on a thermal load basis at just over the rated load"
Our B rated 10A trip seems to trip at under 9A after about 20 minutes.
Soundman


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## listerdiesel (Aug 3, 2012)

soundman said:


> Hi Peter
> You quote "Both types also trip on a thermal load basis at just over the rated load"
> Our B rated 10A trip seems to trip at under 9A after about 20 minutes.
> Soundman


What sort of load is it?

The MCB should carry its rated load, no point in having it labelled otherwise, and 20 minutes does sound like thermal tripping, so it would be worth checking to see if you have a loose connection warming it up, that's quite common.

Peter


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## clive1821 (Mar 27, 2010)

soundman said:


> clive1821 said:
> 
> 
> > Yep it realy depends, i have a 6 way consumer unit in my van some cbs are 6amp and the rest are 10amp but it all is dependant on the supply to your van and indeed what equipment you are using in the van
> ...


Ah ha my truma unit has a 2.5kw worm air heater and a water heater in it which i would think is well over 3kw if both are going which is nearer 16amps perhaps that why your trip is comeing out just have a look at both heat ratings, i tend mostly to use the gas as its much hotter..... just my view dont worry about the mcb rattings as domestic trips are usually bs, peter is corectley quoting all but gets very confusing if you dont understand why and when to use the different types...


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## listerdiesel (Aug 3, 2012)

raynipper said:


> Just a thought Peter.
> I have a 5.5 kva. 240v. to 120v. transformer surplus to requirements.
> I used the last one in our Eagle RV that had a 50 amp supply cord.
> 
> ...


Bl**dy Hell, Ray, that's a small power station!

We could have used that when we were in Greece and the Islands, filming, the caterers were from Hawaii and had all 110V kit, KNOWING they were coming to Europe.....

We found a step-down tranny for them and rigged it up, but they had miles of 3-core flat extension leads which ran pretty hot with the fridges and cooking stuff.

That was on Santorini in 1981. 'Summer Lovers' with Daryl Hannah, she wasn't quite the siren then that she turned out to be.

http://www.imdb.com/title/tt0084737/fullcredits#cast

I'm down there under the Transport Dept, although actually me and John Gott were the lighting electricians, I had the generator and John the lighting truck.

Peter


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## raynipper (Aug 4, 2008)

I do have a few smaller ones Peter.
But the 5.5 kva. in the Eagle managed two air cons, microwave and charging. It sometimes blew a 13a. fuse when connecting on the wrong cycle but I always substituted 35a. fuses..!! 8O 

The smaller ones of 1 and 2 kva. power the US Christmas lights.. :lol: 

Ray.


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## soundman (May 1, 2005)

clive1821 said:


> soundman said:
> 
> 
> > clive1821 said:
> ...


Our Truma is 900w and 1800w.
The ratings (A,B,C) should only effect the surge current!
My problem is the opposite.
I'm beginning to think that the trip could be out of tolerance hence my thinking of separating the circuits and having 2x10a which would still give enough protection.


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## clive1821 (Mar 27, 2010)

soundman said:


> clive1821 said:
> 
> 
> > soundman said:
> ...


Yes ok so thats 2.7kw which is about 12amps with pf correction and depending on actual voltage in any case its very close to 10amp rating of the breaker... either up the breaker rating or try spliting the load.... so i would think the reason for the trip going at 20 minutes is over load of the trip just over the rating


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## cabby (May 14, 2005)

Well can I ask DJMotorhomer, are you any the wiser after 4 pages of information and cross talk and discussion, or is your head spinning. :wink: :wink: :wink: 

cabby

what is the motto. KISS.


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## listerdiesel (Aug 3, 2012)

cabby said:


> Well can I ask DJMotorhomer, are you any the wiser after 4 pages of information and cross talk and discussion, or is your head spinning. :wink: :wink: :wink:
> 
> cabby
> 
> what is the motto. KISS.


Up to a point, I agree, but it is better to sort out the issue and get the correct facts across, so that members have valid information to base their usage on.

Sadly, many fallacies are perpetuated on this and other forums which really need to be discredited.

Peter


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## cabby (May 14, 2005)

Up to a point as you say Peter, but it was a simple question that merely needed a simple answer, just the equation explained would have satisfied his need.
As I said we perhaps should try and use the KISS method.Unless the member wants a full explanation.
Although I do have to say that I am always impressed with the amount of qualified knowledge that is posted on here and thank everyone for it.

cabby


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## soundman (May 1, 2005)

clive1821 said:


> soundman said:
> 
> 
> > clive1821 said:
> ...


I think it would be best to go back to my original question here Clive that nobody has in fact answered as yet.

What is the typical MCB breaker or accumulated value in a MH?

The Truma heater is 900w OR 1800w so as stated I am not consuming more than 9amps but the trip blows after 20 mins. which makes me think the trip may be faulty.


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## listerdiesel (Aug 3, 2012)

In answer to the original question, it depends on what devices you have:.

We have 6A and 10A MCB's:

6A for the fridge and microwave and the 13A socket in the rear section. 
10A for the 13A socket and the Carver 900W element
6A for the charger 
2 spare positions left.

Peter


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## grizzlyj (Oct 14, 2008)

clive1821 said:


> Ah ha my truma unit has a 2.5kw worm air heater


Is that to get them hot and really wriggling before putting them on the hook?


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## soundman (May 1, 2005)

listerdiesel said:


> In answer to the original question, it depends on what devices you have:.
> 
> We have 6A and 10A MCB's:
> 
> ...


Thanks Peter, now we have a result!

Soundman


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## oldun (Nov 10, 2005)

bigcats30 said:


> Watts ÷ Volts = Amps


Though this is undoubtedly correct it is ofte used incorrectly.

If you take a resistive device such as an electric kettle you will be informed that the wattage is (say) 2 kW at 230V and hence the current drawn at 230V will be 2000/230=8.8 amps (exactly as per the equation.

However at a voltage of 100V the current drawn will NOT = 2000/110 =18.2 amps

Why because the wattage of any resistive device is dependant on voltage. It's the resistance than remains the same.

Watts = V timers V divided by Resistance

2000 = 230 x 230 / R and hence R = 26.5 ohm

W = 110 * 110 /26.5 = 457 Watts at 110 amps.

That's why the kettle will take forever to boil water.

So remember the wattage varies with voltage - only the resustance remains constant.


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