# 240v Hookup keeps tripping site supplies



## 90575 (May 1, 2005)

Can anyone offer any advice please?, every time we hook up on site we blow the site trip, not only is this a pain but you would not believe the number of mumbling grumbling site wardens who shuffle away to find the main fuse mumbling something like " blooming american crap"

Anyway, I installed the electrics following advice on these forums thus:

The 240v supply comes in and splits, one side to a consumer unit to power a couple of 240v sockets for tv etc, the other split goes directly to a 7KVA step up/down transformer purchased specifically for an RV to run all the 110v items, we did it this way so that if no hook up was available we could use our generator via the transformer to give us 240V.

We always ensure that the generator is disconnected and everything switched off when connecting but we always trip the rcd's, the only way I have found to connect is to switch off the rcd and main switch on the site post, plug in, switch on the rcd and then switch on the mains but even this can take a few attempts before the rcd will stay on, unfortunately access is not always possible to site posts and that is where the grumbling wardens come in.........

Any advice please? obviously something somewhere is taking a heck of a lot of power on startup, although I will add that once hooked up everything runs fine and we can run just about everything in the van at once with no adverse effect.

I would add that the same happens when we disconnect, if we just pull the plug from the post it trips the rcd, you can imagine grumbling wardens frustration if we do this a few times a week to fill/empty our tanks etc.

So please, any help/advice would be gratefully appreciated.

Many thanks


Ian & Kay


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## Scotjimland (May 23, 2005)

Hi Ian and Kay 

Sorry I don't know the solution only an explanation.. 

Transformers exhibit inrush currents upon initial energisation. In this case, the high currents occur to energise the transformer core. The steady-state magnetising current for a transformer is very low, but the momentary current when the transformer is first energised can be quite high. 

Unfortunately site supplies will normally be protected by C type breakers which are not suited to this type of loading.. which causes nuisance trips.


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## 97993 (Mar 5, 2006)

Sounds like a very likely/plausible cause Jim, if I understand your reply would he be looking for a soft start transformer if such a thing exists, I describe it that way as to me that seems to be what is reqd if i have grassped correctly what you say.
Geo


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## shortcircuit (Mar 19, 2006)

Is it tripping the RCD or MCBs?

Try switching off all your MCB in the RV and then switch on at the site supply. Repeat the exercise with one MCB switched on at a time in order to isolate the possible problem circuit.

Have you had your RV circuits tested by an electrician?


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## oldun (Nov 10, 2005)

My friends have a campsite in france and i spend quite a lot of time with them, some times all season.

I have found that one possible and quite common cause is dampness inside one of the connectors fitted to the motorhome lead, motorhome connectors or the campsite connector.

Could it be a simple as this?


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## 90575 (May 1, 2005)

*thanks so far*

Thanks for your replies so far, just to answer possible solutions we always have everything switched off when plugging/unplugging including all the RV's rcd's, it even happens when red hot and sunny so I wouldn't think damp was the problem, possibly Scotlandjim is right, is it just the transformer pulling such an initial load and is there anyway round it?, has anyone else had a similar problem?


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## Scotjimland (May 23, 2005)

Geo said:


> Sounds like a very likely/plausible cause Jim, if I understand your reply would he be looking for a soft start transformer if such a thing exists, I describe it that way as to me that seems to be what is reqd if i have grassped correctly what you say.
> Geo


Hi Geo 
Soft starts for transformers are available, and a description of how they work is here

http://sound.westhost.com/project39.htm

The size of yorkscouple's transformer will exacerbate the problem.. 7kva is a big trannie.. I use a 3kva which has only had this problem on French 6 amp supplies..


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## 97993 (Mar 5, 2006)

I thought thats how they worked Jim 8O Luvly Luvly 12 volts!!!


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## shortcircuit (Mar 19, 2006)

If you have everything switched off, how can the transformer trip? It must not be isolated!

Please re-read my posting and try and eliminate the problem area. 

MCBs trip with overload and if you have them all switched off this would not happen

RCDs trip with earth faults due to low insulation resistances in cables or [possible neutral to earth faults.

Please attempt to eliminate problem and get some competent advice


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## Scotjimland (May 23, 2005)

shortcircuit said:


> If you have everything switched off, how can the transformer trip? It must not be isolated!


Hi..

The site circuit breaker trips because of inrush to the trannie when it is powered up, irrespective of the load.. isolating the output from the trannie will not affect the inrush, it's a common problem with large transformers.


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## sallytrafic (Jan 17, 2006)

ScotJimland said:


> shortcircuit said:
> 
> 
> > If you have everything switched off, how can the transformer trip? It must not be isolated!
> ...


It would be good wiring practice to insert an MCB or at worst an isolating switch before the input side of the transformer after the point at which it splits from the feed to the consumer unit. 
Why 7kVA, Yorkscouple, thats nearly a 30A supply do you have an electric oven?

I have seen transformers that will limit the inrush to the nominal current capacity of the transformer but again that would approach 30A and a 16A C type breaker would trip. Your transformer might easily draw 200A for 1ms on connection.

Regards Frank

edited for typo


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## shortcircuit (Mar 19, 2006)

I must repeat my first posting.

Please isolate everything by switching off all MCBs and then switch on with one MCB on at a time.

If you are unable to isolate the transformer, then I would suggest you get some advice as to how it should be wired. As Frank has suggested there should be an MCB supplying the transformer on its own.

Can you also make clear if it is the RCD that is tripping or an MCB, for the different possible faults previously indicated


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## damondunc (Feb 14, 2006)

Hi, duncan here,
I have to agree with shortcircuit, about the rcd/mcb trip out which is it that is tripping out? Also I have never heard of such a large transformer being fitted, we have a 3kva transformer on our RV and that trips the 16 amp mcb on the post about 1 time in 10. But there is nothing wrong with the electrics on the RV.The larger the transformer the more chance that this will happen. As shortcirciut says which is being tripped RCD or MCB??or both?mcb tripping indicates too much current, rcd tripping indicates an earthing fault.
cheers duncan.


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## 90575 (May 1, 2005)

*Once again thanks*

Thanks so far for all your valuable advice, to answer your questions we reply as follows

1) We fitted a 7KVA Transformer on advice from these forums last year

2) It is the MCB's that are tripping

From advice so far I am tending to think that it is the initial power rush to the transformer that is causing the problems, would a smaller transformer cure it or is there any other less costly ) way?

Thanks so far

Ian & Kay


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## Scotjimland (May 23, 2005)

Hi Ian and Kay

To recap and as I understand the problem, when you plug in the hook up lead, even with the consumer unit switched off in the RV, you are tripping the site supply .. that being the case it is the transformer that is the problem.. ie.. too big . 
Why you were advised to get a 7kva I can't answer, a 16a supply at best can only supply 3.8kva so you could never fully utilise a 7kva.

Your suggestion of fitting a smaller transformer would IMO be your best bet, a 3kva would be adequate with the least chance of tripping the site circuit breaker.

My suggestion is one of these

http://www.airlinktransformers.com/stepupstepdown-transformers.asp


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## shortcircuit (Mar 19, 2006)

You could fit a type D MCB in your consumer unit in the RV, however as Jim has said earlier on, if the hook-up is a type C, then you would be no further forward.

A smaller transformer may be the solution.


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## LC1962 (Oct 6, 2005)

Jim is right...your transformer is way too big.
We had a similar problem a while back, you really need to downsize.
Call and speak to Airlink, they are extremely helpful.
Cheers
Linda


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## aultymer (Jun 20, 2006)

*Trips*

Please get a qualified electrician to check you rig, in spite of all the well intentioned advice. After all who advised a 7 Kva transformer?
Are you really surprised that site wardens are 'grumpy' when you appear with a rig which you know will lift the breakers and then proceed to connect up anyway?
Please get it sorted just in case I am the next person to meet the overworked and possibly (unpaid) volunteer warden.
Sorry if this contributes nothing to your fixing the problem but sometimes we all have to seek professional help. The cost of this is miniscule compared to the cost of a motorhome or the cost of a fire.


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## speedfreak (Sep 11, 2005)

*240*

hi it sounds like the transformer you are using is to high for site i use a 3000 watt 240 to 110 it runs every thing twin air con ,microwave and has never tripped any site hook up


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## altair (Mar 25, 2006)

It's the inrush current that causes the breaker to trip.
If you have to use such a whopping big lump of iron (how much does the darn thing weigh?) then you could wire a series resistor into the supply lead to the RV to limit the inrush current, then switch it out after one second. A 1000 watt site lamp would probably do the trick. But like everyone has said what on earth are you using 28 amps to run in the RV

Alternatively one of these might do the trick it is a motor filter

Single-phase DIN-rail filter,32A
Manufacturer Schaffner
Manufact. part no. FN2412-32-33

The snag is they are about 133 GBP 
Best to ask your local electrical expert if you are unsure about electricity
as it can be very unforgiving


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## 97770 (Feb 19, 2006)

Hi i have a 5 kva transformer just step down 240v - 120v and a 3 kva 120v - 240v step up from the genset and it has not tripped any mcb's yet, but i think a 3.5 kva step up & down transformer is the way to go. please let us know how you get around this and what works it out ..
good luck,,
FORDY


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## G2EWS (May 1, 2006)

Hi Ian and Kay,

Is your transformer the plug in type as seen on building sites?

If so you may be able to meet up and try someone elses transformer and see if that solves the problem.

Alternatively a friendly builder may loan you a 240 to 110 transformer and once again you could try that.

Finally you could buy one like this:

http://www.hobuk.co.uk/acatalog/CABLES_AND_TRANSFORMERS.html

or

http://www.tlc-direct.co.uk/Main_Index/Site_Equipment_Index/Site_Transformers/index.html

Of course neither will solve your step up problem but maybe you can deal with that as a separate issue or someone else can advise a better product.

Almost certainly the advice given is correct and the transformer appears to be your problem.

Regards

Chris


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## 89338 (May 20, 2005)

I have to agree it's the transformer. When I bought my RV the guy who sold it pointed out this big transformer he had fitted, and low and behold it trips out the MCB's on plug up ( not every time ) but especially in france where you tend to get small supplies. 

Best thing to do is sell it and get a smaller one as advised by others on your replies. As for me it's on the list of things to do, I am half way there as I have a 3Kva waiting to be put in. But you know how it is "a mechanics car always the last to be fixed", I am a electrician and you've guessed it !.

More pressing problem for me to look into at the moment is a cracked windscreen, not a common item in auto glass.

Regards

Lampie


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## zaskar (Jun 6, 2005)

*Re: thanks so far*



Yorkscouple said:


> .......................has anyone else had a similar problem?


Yes, regularly.
We run a Georgie Boy Landau which I THINK has a 5Kva and it has in the past regularly tripped on 1st hook up, more especially on 10amp CL's.
2 tricks I've learned, first, find out if you can get at the trips yourself cos it's a pain for everyone, not to mention embarrasing, if you have to hassle the warden. It's also means you find out what rating the hook up is so that you know what you can and cant have on at the same time.
2nd we always isolate the tranny (we can with ours) and THEN hook up.
then we turn on the tranny and after a few seconds for things to settle down, we turn on the distributiuon box. This invariably works OK.

I've always wondered why trips are locked? I mean, if there's a fault it trips which is what it's supposed to do, and even if you reset the trip and are daft enough to tape it in the open position, the internal mechanism will still trip so you've gained nothing. The only way you can bypass it (I think) would be to fix a jumper lead across the terminals at the back - or fit a bigger trip that you just happened to be carrying around. Surely nobody would be daft enough to go to these lengths.......would they?


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## 90575 (May 1, 2005)

*Thanks for all your help*

Hi all, we are back under bricks and mortar for a few days and we hate it!!! can't wait to be off again, just a thank you to everyone who offered advice on our problems, I replaced the transformer with a smaller 3.5KVA and it has totaly cured the problem, no more tripped circuits no more problems so once again many thanks

Ian & Kay


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## 101600 (Oct 30, 2006)

To make 100% sure that it is what you all expect it to be the transformer. go to maplin buy a clamp on amp meter approx £20 do make sure it is clamp on type and that it is A/C clamp it to your incoming arround the main live cable plug the 240 plug to the mains and check the peak amps ( some meters have a setting to record the max as it can go quite fast)

hope that helps a bit 

oh if you are not confident as always get a pro to do it 

Just noticed you have cured the problem as i was typing this doh


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## oldun (Nov 10, 2005)

*Re: thanks so far*



Yorkscouple said:


> Thanks for your replies so far, just to answer possible solutions we always have everything switched off when plugging/unplugging including all the RV's rcd's, it even happens when red hot and sunny so I wouldn't think damp was the problem, possibly Scotlandjim is right, is it just the transformer pulling such an initial load and is there anyway round it?, has anyone else had a similar problem?


I have worked, for many years, on campsites in France down in the Drome, normally hot and sunny, and it is surprising how often moisture can get into plugs and sockets and cause the RCD to trip, usually one in the site's electrical supply and rarely the one in the caravan/motorhome.

It only takes a couple of minutes to check.


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## sallytrafic (Jan 17, 2006)

*Re: thanks so far*



zaskar said:


> Yorkscouple said:
> 
> 
> > .......................has anyone else had a similar problem?
> ...


Under a proper inspection regime if a trip trips or a fuse ruptures you are supposed to investigate it before remaking/replacing the protective device.

Now I know electricians are the worst offenders but its designed to stop the layman attempting to reset if there is a genuine fault. Repeated tripping does wear them out, repeatedly replacing a fuse is stressing the wiring.

Regards Frank

BTW DJC you have opened an old thread....again.


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## 100675 (Aug 23, 2006)

Here is a link that may help you solve your problem.

http://www.griffin-american-motorhomes.co.uk/tripping.html

Hope it helps.


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