Special locations: vehicle electrics

Discussion in 'Electricians' Talk' started by BiancoTheGiraffe, Jun 3, 2021.

  1. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    Anyone know the deal with overcurrent protection in vehicles which are not caravans/campervans?

    I'm converting an ice-cream van into a mobile bar and originally assumed I'd need to use Double Pole MCBs like you do in caravans and campervans.

    However I can't find anything at all on overcurrent in the regs section relating to mobile catering units.

    Anyone got any experience with mobile installations that aren't living accommodation?
     
  2. Tony Goddard

    Tony Goddard Screwfix Select

    The three where I get my daily burger/bacon buns just have normal CU's rcd and a few regular mcbs, nothing fancy at all. may be right, may be wrong but a real world observation of 3 such units.
     
    BiancoTheGiraffe likes this.
  3. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    Cheers Tony, real world is exactly what is needed!
     
  4. MGW

    MGW Screwfix Select

    I think it comes under section 717 MOBILE OR TRANSPORTABLE UNITS which is similar to caravans, boats etc. So in the main can't use a TN-C-S supply. With 717 there is an exception.
    (i) where the installation is continuously under the supervision of a skilled or instructed person, and
    (ii) the suitability and effectiveness of the means of earthing has been confirmed before the connection is made.
    Fact you need to ask the question I would say TN-C-S supply is out.


    I had not considered the supplies where I work, but they use volunteers, and have 16 amp outlets for caravans, motor homes, and visiting show stands etc. I have never enquired as to if TN-S or TN-C-S supplies. I know at least two supplies maybe three, seems originally part of an industrial estate, and the cost to remove supply was so high they kept the independent supplies.

    I was reading on another forum how some one was going to set up a beer mobile, and wanted to keep the beer cold, and found we have a shed which looks similar to old railway cattle truck which has all the coolers in for use when we have an event. So the beer tent does not have its own coolers it is just placed so beer is stored in the shed with cooler.

    I had never considered the problems when a supply for outside is used for many functions, and I have not looked into if TN-S or TN-C-S supplies, and clearly I should have the answer. As to overload reasonable sure each 16 amp socket is supplied with a double pole MCB and RCD or RCBO.

    But since the safety officer is an electrician reasonably sure it will be all to the regulations. So likely a TN-S supply. But it raises the question of how do visiting attractions ensure the supply is suitable?
     
  5. Comlec

    Comlec Screwfix Select

    If you are converting then you should have access to the regs and as @MGW points out Section 717 is the one you need to comply with.
    You also need to consider other regulations as what you are building is a 'workplace'.

    As for the real world - many 'vans' have working set-ups that may not fully comply but we aware that the first time a kid gets a shock from your van enforcement will be all over you. So best advice read 717 and comply - not really that difficult to do.
     
  6. The Happy Builder

    The Happy Builder Screwfix Select

    I think I would consider fitting DP Devices utter regardless as well as having two lighting and two socket circuits, then if there’s a fault it can be quickly isolated and the bar can stay open, it might be OTT for the doze of the unit but could save a lot of hassle.

    Presumably the supplies will be unknown as it could be supplied from a generator, inverter or a lead from whatever is near by to plug into regardless of earthing type?
     
  7. MGW

    MGW Screwfix Select

    I have never worked out how to detect if the supply is TN-S or TN-C-S. We are told ELI maximum 0.8 ohms with TN-S and 0.35 ohms with TN-C-S but that is not a reliable method, and at the 16 amp socket as long as better than 2.87Ω it may pass as TN, over 2.87Ω we assume TT.

    Even at the head often no way to know unless the DNO have affixed a sticker.

    The 3 kVA isolation transformer seems great, but big question is where does the earth go? If the earth is not isolated then pointless, and if it is where is the TT earth connection and the RCD?

    I would say one of these [​IMG]the EZ165 and if the ELI is over 10Ω then likely TT so OK, if under 10Ω than need to ask questions. It seems wrong way around, it is low ELI which is the problem, want it between 10Ω and 200Ω.
     
  8. The Happy Builder

    The Happy Builder Screwfix Select

    You cannot isolate an ice cream van bar from the ground it stands on it’s too big.

    The best protection for the users is an installation installed and maintained to a high standard with regular PAT for all the appliances.
     
  9. The Happy Builder

    The Happy Builder Screwfix Select

    An ice cream van bar is also too big to be supplied from a portable tool isolation transformer, they are intended for supplying individual power tools, not small installations.

    If it’s a bar you could use a 110 volt installation and equipment as within many pub cellars, they don’t isolate the installation from the supply earth, but do create a new earth loop and of reduce the voltage so generally a single fault will only create a touch voltage of up to 55 volts, if you do you will really need DP circuit protection, which is what you are trying to determine is needed anyway.

    The odd bits of electrical work I have done in pubs didn’t really need me to get involved with the dispensing equipment because most of it is leased or on loan from the breweries, emergency lights in the toilets was more my area of expertise along with deep fat fryer supplies. If there was a problem involving cellar equipment I generally just turned it off and told the landlord to ring the brewery.

    This seems like it is really more of a BS7909 question than BS7671.
     
  10. The Happy Builder

    The Happy Builder Screwfix Select

    @BiancoTheGiraffe you are right, I cannot find anything to say you need DP MCBs.

    @MGW you can use an isolation transformer, but it needs insulation monitoring in the installation or you have to TT it and have an earth electrode, which could be an issue in many locations 717.413
     
  11. The Happy Builder

    The Happy Builder Screwfix Select

    It might be worth considering buying one of the IET guides:

    https://www.napitdirect.co.uk/p/iet-practitioners-guide-to-temporary-power-systems

    Life will be a lot easier if it’s run off a generator as the earthing arrangement won’t vary between locations, the IET says each socket needs its own 30 mA RCD, so RCBOs seem to be the way to go with an upfront time delayed RCD, in the van not at the generator. The generator can use electrical separation as a protective measure if it’s a small unit, so maybe an isolation transformer can be considered, there seems to be a mix of advice depending on which IET book I look at.

    Isolation of both live conductors can be achieved by pulling a plug out.

    As most of the events I have been involved with have been on farms with TT earthed installations I have rarely had to get over over concerned about the earthing arrangements.
     
    spannerw likes this.
  12. MGW

    MGW Screwfix Select

    Can't see how that helps? it is not the live wires which are a problem, it is the earth.

    With a TN-C-S installation if the PEN that's the earth and neutral where they are combined is lost, the voltage will swing from 0 - 400 volt if step down transformer is three phase, and the earth wire anywhere between 230 volt and true earth, it is rare I know, but this is why petrol stations, caravans, and boats can't have a TN-C-S supply.

    With electric cars they use an isolator with cuts first lives (line and neutral) then earth if voltage goes out of the range of 207 to 253 volts, and it is claimed that means no more than 70 volt to true earth, not sure what happened to the 50 volt limit quoted for years.

    Nearly all garden equipment is class II so there is no earth.

    If all in the building is bonded then if the bond is 230 volt from true earth no problem, same as birds on the electric cables, the problem is when you enter or leave the building, old never step off a derailed tram, jump. There is the voltage problem but that is not the issue here, equipment burning out due to over voltage should not be a danger, just an expense and as long as the threshold is non conducting and not earthed no real danger. Biggest danger is where the gas has be earthed on wrong side of isolating block.

    When the meters are outside or other earthed items like stop taps and cast iron drains, any other earthed system needs to be far enough away so the voltage gradient is low enough, fire regulations from memory means a caravan needs to be at least 2.5 meters from a building, so in a caravan site the reception building can be TN-C-S but all caravan hook-up points are TT.

    Boats often don't import earth and use an isolation transformer or have diodes in the earth to stop electrolyte action.

    But I have I will admit not really considered where I work, we have 16 amp outlets to plug 110 volt transformers into, and on a gala these are often used by visiting attractions, steam organ, hot dog stand etc. Also during the pandemic people volunteering have been using caravans and motor homes plugged into these outlets rather than use the accommodation cottage.

    I have never enquired as to supply type, it may be TN-S in which case no problem, in fact considering the size very likely TN-S, and since our safety officer is an electrician seems unlikely he would have missed it.

    But if he is not around, I would be next to ask, and I have never looked into it, so it is likely at many events finding if the supply is TN-S or TN-C-S is not as easy as it sounds, and knocking an earth rod through tarmac or concrete does present a challenge.

    The watch my back option is the generator. So we are looking at upload_2021-6-6_0-14-26.png in BS 7671.

    In real life it is very unlikely the PEN will be lost during an event, and one can likely get away using a TN-C-S supply for years without a problem, but there has been a surge in the use of outdoor electrical equipment, these upload_2021-6-6_0-20-20.png are becoming popular the advert says nothing but the user manual states it is a Class I appliance and must be earthed. Lawn mowers etc are normally class II so are not earthed so no problem, but is it safe to use a class I item in the garden when you have a TN-C-S supply? I would say no, that patio heater is only suitable with a TN-S or TT supply if used in the garden.
     
  13. The Happy Builder

    The Happy Builder Screwfix Select

    For years we did bars without any electricity, just a some trestle tables, bottles, barrels and gas bottles, the biggest issue was washing the glasses, now the glasses will be disposable plastic.

    These events were either indoors or marquees, but generally on farms with TT earthed installations, so I didn’t have to overthink things regards earthing and double pole isolation was provided by the DP RCDs.

    The types of earthing arrangement that could be used with this van could be TNS, I-S or IN-S if supplied from a generator, TNS or TT if supplied from a fixed installation, but TNC-S should not be used.

    So I am not claiming any specialist knowledge, but to cover all eventualities I would go for an upfront time delayed 100 mA RCD that needs to trip within 200 milliseconds then the new compact Wylex Type A Double Pole 30 mA RCBOs with one for each socket, fixed appliance and circuit.

    Avoid anything that is Class I and needs earthing.
     
  14. The Happy Builder

    The Happy Builder Screwfix Select

  15. Comlec

    Comlec Screwfix Select

    Whilst informative I don't know what 'temporary supplies' has to do with the OP's original question. The whole point of the regulations covering the construction of Caravans and Mobile units is the supply is unknown!
     
  16. The Happy Builder

    The Happy Builder Screwfix Select

    Quite, the earthing system is unknown.

    The earthing system dictates if the neutral needs to be disconnected, as the earthing system is unknown then I am saying use double pole MCBs or RCBOs, personally I would use DP RCBOs.

    Once the bar is set up at an event then BS7909 needs to be considered as well and if you get a copy of the IET practitioners Guide you will find it contains guidance on how to wire the van.

    There's more things to consider other than just BS7671, including BS7909 and the EAWR.

    In amongst everything else the bar owner doesn't want to lose power just when they are at their busiest, and possibly lose a very large amount in takings just because one silly little fault has knocked the whole unit out.
     
  17. Bob Rathbone

    Bob Rathbone Screwfix Select

    If you want to reduce the touch voltage between the van and true earth, fit a local earth electrode and cover the top as required by the regs. As for the type of supply, TNS or TNC-S, it is irrelevant, what you must remember is not to use the earth supplied by the DNO, use a local earth electrode and cover with 30mA RCD, you will then have a 'clean earth' with no possibility of importing a voltage from a fault on the supply system. Identification of the supply can usually be made at the service head or cut out, look at where the main earth is connected, if in doubt assume a TNC-S and follow the advice above.
     
  18. The Happy Builder

    The Happy Builder Screwfix Select

    I have actually met James Eade and listened to a presentation he gave along with Paul Chaffers followed by a question and answer session similar to the one in the webinar, then stood and had a chat with James over a cup of coffee.

    Buy the IET Practitioners Guide, I have that and the other book James authored, the Practitioners Guide is the cheapest and the most practical of the two books.

    If you are getting involved with outdoor events and outdoor events equipment you are going to do things differently to how you do in fixed electrical installations, I am aware there are differences in the way things are done, but I'm not any kind of expert, I was going to go on the three day BS7909 training course that James runs but eighteen months ago events stopped when Covid closed the venues down, maybe I will get around to it later this year or next, who knows? The way things are at the moment there doesn't seem any point in rushing to book the course, one of the venues I was lining myself up to work at doesn't even operate anymore, the event industry guys have been hit really hard.

    If the bar is booked for any sort of fairly serious event all the paperwork will have to be in place and kept up to date.

    Make sure you use a suitable cable to wire the internal installation in the van as well, insulation is the primary protection in these units, everything else is there in case the insulation fails as secondary protection.
     
  19. The Happy Builder

    The Happy Builder Screwfix Select

    and if the mobile bar knocks out the supply to a stage, sound system or the like you aren't going to be very popular!!
     
  20. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    Thanks for the replies, unfortunately for me the end client have now cancelled the project (which is immensely inconvenient as we've done most of the hard work!)

    I had settled on DP MCBs regardless of the lack of mention in the regs, and was going to send an earth rod out with the van, regardless of the supply it was connected to.

    Interesting that people have mentioned Mr Eade, I did his 7909 course years ago, before it became C&G. Top man, very very knowledgeable!

    I've got his book, but didn't think to look at it for vehicle electrics.

    Client are talking about doing a large American style RV conversion instead, so I may well be looking at the installation for that in a month or so
     

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