Truma 3002 tripping electrics

[ianhoughton]

I've got the van at the house to get ready for going away later in the year. When testing the heater (Truma 3002) with the van connected to the house electrics, its tripping the RCD in the main house fusebox. This happens roughly 1-2 minutes after turning the heating on (it doesn't matter if its on the 500,1000 or 2000w setting).

After speaking with Gary @ arcsystems, he suggested I test and/or change the 125 & 175 Temperature control devices (as their quite cheap). I've changed these this morning and the issue is still there. The heating element starts to get hot, but always trips out after a while. Is it worth changing the heating element or biting the bullet and getting someone out to look at it?

 

[Dustydog]

Ian
Leaving the heater off have you tried using other mains appliances eg a vacuum cleaner plugged into the caravan hooked up to your house? If the home RCD trips it could be your EHU lead.
There have been cases of the plugs on the Orange EHU lead being faulty.

 

[ianhoughton]

Yes, I tried our 2400w fan heater to test that the van RCD & lead were ok. The fan heater works fine.

 

[ProfJohnL]

Hello Ian,

Gary's knowledge and advice is usually very good, so I am sure his suggestion of checking the temperature control devices is based on practical experience of something that has happened before, but the symptoms you describe make me think the problem may lie somewhere else.

Firstly it is strange the RCD in the house trips before the caravans, This suggests it may be something to do with the EHU connections as Dusty suggests, but I would normally expect this to happen immediately the power is turned on, and not after a few minuets. I suggest you do get the caravans power circuits checked for correct safety operation.

As the problem only seems to arise when using the Truma electric elements and after a few minuets rather than immediately this points to heater being suspect. In other work I have done with heating elements I have come across electric elements where a similar delayed problem occurs.

I don't know if you understand what or how an element works, but in essence what you can see is an earthed metal shroud, which contains a mineralised electrical insulator with the actual heating element running concentrically through it.

In use the central heating element gets hot and the heat is supposed to be conducted away by the mineralised insulation and transferred to the outer tube. Unfortunately as the central element becomes hot, and being a metal, it expands, and that expansion has to be accommodated inside the mineral and outer tube. With continued element expansion and contraction, the element will rub on some of the mineral, and may work its way through it to make contact with the earthed outer tube. When cold and pulled away from the outer tube kit will displaying normal test results, but in its hot and expanded form it only needs to touch the outer tube to produce the fault current and trip the RCD.

This type of fault will often occur if an element has been physically damaged or where it has been bent to shape.

Depending on where the fault is along the elements length, such a fault will not always trip the over current MCB's.

You may need to get the elements replaced.

 

[Damian]

Quote " Firstly it is strange the RCD in the house trips before the caravans,"

There is nothing strange about it at all, it is normally the case.
That is why an unprotected supply is needed to test caravan electrics.

 

[ianhoughton]

Thanks everyone for the advice. I didn't mean to come across as not appreciating Gary's suggestion, it's nice to find someone willing to discuss an issue over the phone without any prior commitment, top man !!

Looks like I'll be trying a replacement element next.

 

[gary]

Hold the phone!

Not sure I said change them out of hand so to speak?, more they are always highly suspect for this and indeed other faults, so the first thing to check because of this inherent weakness and probably also said nothing lost in changing them.

On the other hand, the elements are 99.9% bomb proof so unlikely to be at fault, least I've had a dozen pairs for years and not managed to sell one set!. Checking them though is easy

S I feel sure I also suggested more possibilities, perhaps then another phone call to refresh?

 

[bertieboy1]

Have to disagree with you Damien,it is not normally the case.The only reasons for a house RCD to trip first is -
1.The earth fault location is after the house RCD and before the caravan RCD.
or
2.The sensitivity of the caravan RCD is higher than the house RCD
To test for an earth fault instruments are used without any electrical supply connected.

 

[Damian]

You can disagree as much as you want to.
I know from dealing with tripping electrics that either the house or site bollard will trip before the van.
That's not maybe, possibly or it cannot happen, it does regularly.

 

[GStockton]

Quite correct Damian, considering that the fault current that is required to trip the rcd mounted in the caravan ( normally between 22.5 to 30 Milli amps ) has to first pass through the House rcd first. I take it that you use an Isolating transformer for your servicing work to eliminate re setting the householders rcd when testing the caravan? I know a few Mobile engineers with these.

 

[Damian]

I use a referenced sine wave generator for testing purposes.

 

[ianhoughton]

Well I'm glad to report that replacing the heater element at the weekend has cured the fault. Got nice and toasty yesterday and the electrics stayed on without tripping out.

Thanks folks.