# Electrical cut out thingy - 240v



## gillnpaul (Jan 6, 2007)

Hi Electrcal type people
Is there such a gadget on the market that is connected into your mains electrics in the van that can be set to cut out before the site electrics have tripped. So, if for example you are staying on a site with 5amp EHU, you can set your trip to cut out at say 4.8amp, therefore you only have to reset your breaker, not the sites, and it needs to be adjustable, to other site power limits. I would want this piece of kit to have a built in ammeter in it as well to monitor my power usage. Are these things available and if so what are they called and where can I get one.....
Thanks
Paul


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## DABurleigh (May 9, 2005)

Reich and Ivra used to do one. Haven't seen a separate thingy around for a while. Functionality is built into some Victron boxes.

http://www.motorhomefacts.com/ftopicp-528441.html#528441

Dave


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## 91502 (May 1, 2005)

Hi 
I am not an expert but I think they will both trip. 
We have a separate distribution boards in our log cabin and also one in the conservatory as both feed power to things outside, if either trip out then the RCD on the main board also trips. 
I am sure someone will give a reason. 
James


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## spykal (May 9, 2005)

Hi

It is not something that I have tried but you may be able to use an energy monitor to display exactly what amount of electrical power you are using at any time ...that would allow you to work within the site power limits. These units are designed to be used in a domestic situation but I cannot see why one could not be set up in a motorhome. They work wirelessly and transmit the power being used from a sender that is clamped onto the incoming live wire, you can position the display unit somewhere easily seen.

One like this may do it : 
Energy meter <<<

Mike


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## gillnpaul (Jan 6, 2007)

Thanks for all your helpful replies guy's...I just thought that this would be a really useful piece of kit. If you look at the temp sites in London for the Olympics, they are supplying 6a only, what's that a kettle and the microwave, put on something else and...Hey Mr Warden, "can you reset my breaker please", whereas fit my idea and just do your own reset. I know the piece of kit your talking about Spykal, £16 from Maplins, but its just a monitoring device (which is better than nothing), and if there is nothing on the market thats the way I'l go.
Just to answer your suggestion Jp, why do you think they will both trip?
If site supply is 6a and you set your trip to say 5.5a , why should you trip out the site EHU ?

Regards
Paul


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## Chudders (Jul 5, 2008)

Very complicated to explain but it depends on the the ' characteristics' of the CPD (circuit protective device) in question.
Most circuit breakers will 'hold' more than their maximum stated overcurrent load for a short time. (This is different from Fault current) There are different types of circuit breaker (Type B Type C or Type D as examples and others) Some are designed to hold a higher current in particular circumstances as for instance when items initially energise. Motors for instance pull considerably more current on start up and so often a Type C breaker is used to prevent nuisance tripping although it may still be a 16 Amp breaker for instance. 
You would need to know the type of breaker on the site hook up, probably Type B. It will say on the breaker. 
Much consideration has to be given when designing electrical installations generally including what is known as co-ordination of protective devices. So that selectivity between the protective devices depends on the co-ordination of the operating characteristics of the two protective devices so that when a fault current occurs only the device intended to operate does so.
In your suggested circumstances a 5.5Amp breaker (if there were such a thing) is unlikely to be much different from a 6 amp breaker. Either or both may disconnect depending on the above considerations. There are variable circuit breakers used in industrial applications after full circuit design condsiderations. They are very expensive and can only be used in certain circumstances. Not suitable in your case.
More important is that you regularly check the operation of your RCD.
Hope that helps.(or not )! !
Dave.


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## gaspode (May 9, 2005)

gillnpaul said:


> Just to answer your suggestion Jp, why do you think they will both trip?
> If site supply is 6a and you set your trip to say 5.5a , why should you trip out the site EHU ?
> 
> Regards
> Paul


I think JP is confusing an RCD trip with an overload trip. Certainly it's common to trip an RCD "down the line" in addition to the most local one but we're not talking RCDs here are we? RCDs trip the supply on detection of an earth fault, not an overload.

With MCBs (overload trips) it is possible to trip a down the line one but much less likely. It all depends on the time/load characteristic of the trip. For instance in the example, a 6a MCB might well trip before a 5.5a one (if such a thing existed) because there is usually a time factor built in to allow for overloads which last a fraction of a second, common when switching an appliance on or off. ie: the 5.5a MCB might tolerate a small overload for a fraction of a second longer than the 6a one so the 6a might trip first - you'd need a greater current differential which in turn would curtail your available power.
In practice, if you installed a 5a or 6a MCB in the motorhome it would be a toss-up whether that would blow before the site MCB or not, and if you installed a 5a one you'd lose 17% of your available power before you start.

It's not rocket science really and you shouldn't need any monitoring device, you just need to understand the power used by your appliances. A 6a supply will allow you to use appliances totalling 1440 watts (1.44kw), easily calculated using the formula: watts=volts x amps, so 1440=240 x 6.
1440 watts would equate to a low power domestic kettle or a mid-power microwave - not both at once. Normal domestic kettles will consume between 2000 and 3000 watts!!! Look on the label underneath, the power in watts or Kw is always marked. Also don't use the output power of your microwave to calculate the power used, an 800w microwave will often consume as much as 1500 watts, again the label on the back will tell you exactly.

Don't forget to allow for the power being used by the battery charger (allow at least 150 watts) and your TV (around 50 watts for a small TV and 20 watts for a freeview/satellite receiver) and your lights (count the lights in use and multiply by the bulb wattage).

Mikes idea of using a domestic energy meter might be a good suggestion if you don't want to "do the maths" but bear in mind that these devices work by taking a sample reading every few seconds (typically 6 sec) so by the time the meter displays an overload it'll probably be too late - the circuit will have tripped.


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## Chudders (Jul 5, 2008)

Gaspods explanation of checking the load being used is a good and cheapest option. If you plug in a kettle unplug the fire first as an example. 
Dave


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## lgbzone (Oct 8, 2008)

Just a heads up if you try the energy monitor thing; we have one at home that was given to us by our supplier, on the input to the consumer unit (at home) it works fine, but if you try clamping it around a ring main or anything like an extension lead, it doesn't work.

I put this down to the fact that the main cable that it will work on is far thicker than the others, I don't know how thick the cables are in the motorhome, but I suspect ours wouldn't work in the van.

HTH


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## spykal (May 9, 2005)

lgbzone said:


> Just a heads up if you try the energy monitor thing; we have one at home that was given to us by our supplier, on the input to the consumer unit (at home) it works fine, but if you try clamping it around a ring main or anything like an extension lead, it doesn't work.
> 
> I put this down to the fact that the main cable that it will work on is far thicker than the others, I don't know how thick the cables are in the motorhome, but I suspect ours wouldn't work in the van.
> 
> HTH


Hi

I think you will find that it needs to be around just the live feed....if you clip it around a cable that has live, neutral and earth it will register nothing :wink:

Mike


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## lgbzone (Oct 8, 2008)

spykal said:


> lgbzone said:
> 
> 
> > Just a heads up if you try the energy monitor thing; we have one at home that was given to us by our supplier, on the input to the consumer unit (at home) it works fine, but if you try clamping it around a ring main or anything like an extension lead, it doesn't work.
> ...


Thanks Mike

I'm very good at what I do, but as you may have guessed; I'm not an electrician :lol:

Lee


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## DABurleigh (May 9, 2005)

Bet you know how to take care of a matched set of nicads, though ;-)


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## lgbzone (Oct 8, 2008)

DABurleigh said:


> Bet you know how to take care of a matched set of nicads, though ;-)


That's true, and LiPo batteries which is far more important as the consequences can be disastrous.

Just a little bit of self esteem restored


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## gillnpaul (Jan 6, 2007)

Wow Guy's

What a learning curve this forum is, Thanks to everyone who answered my query, I honestly didn't think it would be that hard to do, but you live and learn.
Looks like a monitoring device then, and at least if we are going to , for example , use the microwave, we weill be aware how much power we are currently using, and if we would have to turn something off if we want to hoover the van out. (or should I say...Gill wants to hoover the van out).

In my ideal little world every site would be the same power output, and there would be no problem .

Thanks again
Paul


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## tonyt (May 25, 2005)

Of course, if you'd all taken more notice of my wireless hook-up thread earlier this year, around April as I remember, you wouldn't have any of these problems.


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