Static caravans and air conditioning.

[GHJT]

Hi Guys.

Here's a good one for you, to rack the techies brains out there. Any views on the following please? By the way I'm NICEIC approved, Q.S. MIET status with IET. Been doing if for years.

I have telephoned NICEIC technical today but as always there are unanswered vagaries surrounding my question. So here goes. I do some EICR's for a famous brand leisure park. Static caravans. Some of the caravans have had 2 part air-conditioning units fitted. My gas safe colleague condemned and cut off the gas to some caravans/static homes as the air-con is failing the `gas spillage test'. He says this is actually RIDDOR reportable.

Anyway, this got me looking at the air con units myself. Outside part is mounted under the caravan, bolted to uni-strut to the concrete base. Micro-bore copper tubing then goes to the 2nd part of the air con unit inside. To get around the air con guy not having any electrical qualifications, he simply puts it on a plug so he can say it's a mobile piece of equipment. (He's wiring is horrible by the way, wires the plug with 4 core HO5vv cable, and cuts a core off at the plug leaving copper showing and not entering the plug). Anyway, so leaving an exposed conductive part, C1 etc etc....

So anyway, my thoughts regarding the pipework were, extraneous conductive part entering the caravan (micro-bore copper), copper needs earth bond back to MET. Reg 411.3.1.2 Bearing in mind this is a caravan in a caravan park, so a special location, within a special location. Section 708 and section 721.

I have also referred to Guidance note 8 on Earthing & Bonding.

Now the NICEIC tech tells me whether or not it is an extraneous conductive part all depends on whether or not I measure 23000 ohms from the MET to the copper. Ok, so if it's less, then I bond it, if it's more then it's `just a piece of metal' and it isn't extraneous. Well that's all well and good, but there's other things to take in to consideration, like the famous TT weather scenario

That might read 10 ohms on a nice wet day, or 500 or more on a dry summers day. Or no earth at all in dry clay. So if I measure from caravan MET IR test and get more than 23000 ohms today on a nice hot day then I don't bond it as it's showing as non-extraneous and just a piece of metal. But what about when it's poured with rain, or snow, the concrete base is soaking, the uni-strut that it's mounted on is soaked and and there's rain dripping off of the air con unit and micro-bore copper. Bearing in mind the metal chassis and tin covering of the caravan, which in some cases the copper rubs against. So if I ran my tester from MET to micro-bore copper on that day I may get an entirely different reading and less than 23000 ohms and therefore it IS extraneous as the weather has had an effect. NICEIC tech says if I bond something non-extraneous then I may be introducing a potential that isn't there.

So my question is, like with TT, different days, different scenarios. Do I bond back to MET or not?? My view is that I should. Under 16th we bonded anything and everything, even if it looked shiny Any thought's gratefully accepted!

With thanks,

Gary T

 

[Leesparkykent]

Is the microbore copper exposed within the caravan?

 

[Marvo]

The pipework for a split air con unit is usually connected to a solid flare fitting at both ends and should be at earth via the CPC of the supply. Are you worried about the pipework being extraneous when the unit is disconnected?

Has the installer breached manufacturers installation requirements by using a plug rather than a permanently wired switched spur?

 

[Marvo]

Also the pipework is usually shrouded throughout its entire length in half inch thick closed cell insulation....

 

[GHJT]

Is the microbore copper exposed within the caravan?

Hi Lee. Thanks for your quick reply. They are generally in a plastic trunking, but so far we've found out he's done about 120 of these so it's under investigation, so there may be variations we've not come across yet. Brought to my attention due to failing gas safe, but the big electrical concern is that in effect a caravan is essentially one big metal shed in a wet field.

 

[GHJT]

The pipework for a split air con unit is usually connected to a solid flare fitting at both ends and should be at earth via the CPC of the supply. Are you worried about the pipework being extraneous when the unit is disconnected?

Has the installer breached manufacturers installation requirements by using a plug rather than a permanently wired switched spur?

Hi. Thanks for your quick reply. I think you have raised two good points there. One is that in my mind it should be a fixed unit, but he can't alter the electrics and add a fused connection unit, as he isn't qualified, so if the plug is pulled, then you are correct, the pipework enters the caravan and the cpc does nothing. The big electrical concern is that in effect a caravan is essentially one big metal shed in a wet field. Reg 411.3.1.2 is clear, but determining whether it's actually extraneous or not is less so. I personally think it is and should therefore carry a bond. Thanks for your reply!

 

[Marvo]

Just for interest how is the gas spillage test performed? I'm not in the UK so it sounded to me more like a test you'd do on a flue system to detect leakage of carbon monoxide.

 

[Leesparkykent]

Hi Lee. Thanks for your quick reply. They are generally in a plastic trunking, but so far we've found out he's done about 120 of these so it's under investigation, so there may be variations we've not come across yet. Brought to my attention due to failing gas safe, but the big electrical concern is that in effect a caravan is essentially one big metal shed in a wet field.

If they are covered by trunking I don't see a problem as not accessible to the touch between exposed conductive parts and extraneous conductive parts (if they are deemed to be extraneous).

 

[GHJT]

Just for interest how is the gas spillage test performed? I'm not in the UK so it sounded to me more like a test you'd do on a flue system to detect leakage of carbon monoxide.

Hi, thanks. The Gas Safe engineer demonstrated this part of his test for me to understand from an electrical perspective. On the gas fire in the living room he lights a `smoke match' and runs that under a part of the the gas fire, I think he called the smoke diverter. The smoke is then meant to get pulled up the flue and expelled. With the air conditioning unit running, it pulled the smoke away from the gas fire and across the room and the smoke didn't go up the flue. Yes I'm sure it would also have carbon monoxide implications as well. Very good point you have made. Thanks!

 

[GHJT]

If they are covered by trunking I don't see a problem as not accessible to the touch between exposed conductive parts and extraneous conductive parts (if they are deemed to be extraneous).

Thanks Lee. That is a good point in as far as being covered. However, in my house neither the water stop cock are accessible or the gas pipe as they are behind cupboards, but nonetheless, they are still required to be bonded by earthing & bonding regulations. I accept that it's unlikely to be touched, however, what about in the event of a fault on the unit? Does the air con unit come live, will the uni-strut come live. Will the caravan chassis or tin covering. A whole mine-field here in my opinion. Thanks for your answer. Gary

 

[Marvo]

Ahh, so the caravans have a gas fire in them as well. Makes sense.

 

[GHJT]

Ahh, so the caravans have a gas fire in them as well. Makes sense.

Yes indeed. Some don't though, they have electric heaters, but they all have a boiler or water heater of some description for hot water and LPG gas cookers for cooking. The gas engineers carries out various spillage tests on whatever units have a flue to ensure the flue is expelling correctly and he carries out a parts per million Carbon Monoxide test too. Don't know too much about the intricacies of that one though. Thanks for your time!

 

[Leesparkykent]

Thanks Lee. That is a good point in as far as being covered. However, in my house neither the water stop cock are accessible or the gas pipe as they are behind cupboards, but nonetheless, they are still required to be bonded by earthing & bonding regulations. I accept that it's unlikely to be touched, however, what about in the event of a fault on the unit? Does the air con unit come live, will the uni-strut come live. Will the caravan chassis or tin covering. A whole mine-field here in my opinion. Thanks for your answer. Gary

An extraneous conductive part is a conductive part liable to introduce a potential, generally earth potential and not forming part of the electrical installation.

If covered with plastic trunking how liable is this to introduce a potential?

If the indoor/outdoor unit is an exposed conductive part rather than an extraneous conductive part then they should be earthed not bonded. The purpose of bonding an extraneous conductive part would be to ensure extraneous conductive parts and exposed conductive parts are at the same potential. If the extraneous conductive part is covered in an non conductive covering its no liable to introduce a potential.

 

[ruston]

Ahh, so the caravans have a gas fire in them as well. Makes sense.

In the days of the fashionable ceiling recirculating fans it was not allowed to have them in a room containing an open flue gas appliance.

 

[GHJT]

Yes you're first paragraph is exactly word for word from definitions and I agree with what you have said. However, below and underneath the caravan, the pipes are not entirely covered by plastic trunking before entry. They do have some foam insulation in places, but not all. Plus in places they touch against metal chassis work and they get wet. You are also correct about the difference in Earthing & Bonding and I am sitting here right now with guidance note 8 in front of me. Either way, page 55 of 17th AM3 says the following
Regulation 411.3.1.2 Protective equipotential bonding:
In each installation main protective bonding conductors complying with Chapter 54 shall connect to the main earthing terminal extraneous-conductive-parts including the following:
( i ) Water installation pipes.
( ii ) Gas installation pipes.
( iii ) Other installation pipework and ducting
( IV ) Central heating and air conditioning systems.
( v ) Exposed metallic structural parts of the building.

It is a piece of class one electrical equipment and therefore not double insulated and although I doubt the wall mounted air con units are liable to introduce a potential, if the compressor is sat on the wet floor underneath a caravan on the wet concrete, then I would argue that these set-ups possibly can. Either way, in my view it should be either Earthed or Bonded, depending on how tackled as once the plug is pulled and the CPC is removed then it has no earth protection of any sort.