Distribution box from 32amp generator supply?

[BarryConvex]

Hi all,

I run a small event marquee which has recently been bumped up to a 32 amp requirement by the addition of an electric urn. I need to distribute the power around the marquee but being an ex engineer I would rather make a PATable distro box than blow £200ish off the shelf.

During research I found a paragraph in official literature which said there is no obligation for "safety devices" on outdoor equipment up to 32 amp. My PAT man suggested I build a consumer unit board anyway and I'm inclined to agree, for safety sake.

However, I have had experience of inline RCDs over reacting when used off a generator. Anyone have any comments about RCDs and generators? Could this be due to voltage drop over my 100m 6mm2 cable? Fluctuating supply?

If this is the case I'm inclined to wire 3x 13amp 6gangs into the 32amp cable via a sturdy 60amp connector box or something. Maybe a IP65 junction box. Basically it's about £5 because I have all the other pieces.

So
1) Is the cheapest option legit and PATable? (although at the cost of safety devices)

2) If not, any comments on RCDs with generators and suggestions for consumer unit config? (eg. 40amp 30ma RCD, 2x 16amp MCBs, 2x double sockets)(or RCDs on the sockets instead of the board)

Any input at all on this would be useful and appreciated.

Ta.

 

[ban-all-sheds]

being an ex engineer I would rather make a PATable distro box than blow £200ish off the shelf.

//www.diynot.com/forums/viewtopic.php?p=1259321#1259321

Could this be due to voltage drop over my 100m 6mm2 cable?

As an ex-engineer, do you think that 25V drop is acceptable?

Any input at all on this would be useful and appreciated.

http://www.rubberbox.co.uk/on-the-shelf/index.php

 

[electronicsuk]

During research I found a paragraph in official literature which said there is no obligation for "safety devices" on outdoor equipment up to 32 amp. My PAT man suggested I build a consumer unit board anyway and I'm inclined to agree, for safety sake.

If anything, the requirements for a temporary electrical installation such as yours will be far more stringent than a typical fixed installation. I'm not sure what literature you read, but it sounds incorrect to me.

However, I have had experience of inline RCDs over reacting when used off a generator. Anyone have any comments about RCDs and generators? Could this be due to voltage drop over my 100m 6mm2 cable? Fluctuating supply?

It's probably something to do with poor earthing arrangements. What are your arrangements re earthing at the generator end? Are you using (and testing at every job) an earth rod at the origin of supply?

If this is the case I'm inclined to wire 3x 13amp 6gangs into the 32amp cable via a sturdy 60amp connector box or something. Maybe a IP65 junction box. Basically it's about £5 because I have all the other pieces.

So
1) Is the cheapest option legit and PATable? (although at the cost of safety devices)

Well, as an engineer, you tell me if you think it would be a good idea to have a 32A supply split off in a junction box without fusing down to 13A socket strips which are fitted with unprotected 1.5mm^2 flex?

2) If not, any comments on RCDs with generators and suggestions for consumer unit config? (eg. 40amp 30ma RCD, 2x 16amp MCBs, 2x double sockets)(or RCDs on the sockets instead of the board)

Any input at all on this would be useful and appreciated.

Ta.

As per BAS above, go with a rubberbox distro. I would also suggest you buy a copy of BS7671 and have a read of at least section 711, and perhaps sec. 740 if you consider it relevant to your work. That 6mm cable also needs to go, at a guess I would say that you'll be needing 16mm^2 as a minimum, possibly more.

 

[ricicle]

551.4.4.2

 

[ericmark]

I would guess it would come under Section 711 Exhibitions, Shows and Stands which have extra rules?

711.410.3.4 tells us a 300ma S type RCD is required at the generator.
However 711.411.3.3 says with 32A socket outlets or less 415.1.1 applies i.e. 30ma at 40ms.
If no fire alarm is fitted then you are also restricted as to cable types see 711.521 and to comply with IP4X not sure on the use of 13A plugs and sockets? 711.55.7 refers to water ingress.

During research I found a paragraph in official literature which said there is no obligation for "safety devices" on outdoor equipment up to 32 amp. My PAT man suggested I build a consumer unit board anyway and I'm inclined to agree, for safety sake.

Think you have that wrong way around larger than 32A you don’t require RCD protection for 32A and below it is required.

As to in-line RCD’s don’t think you will be able to connect them to the appropriate cable the flame retardant armoured power cable
I have seen would not fit the in-line RCD’s so some form of dis-box will be required.

I have seen SY Braided Cable used and although not quite to standard as to fire resistance I would not foresee any problems.

It will need inspecting and testing and as BAS points out the last thing anyone wants is after it is all laid out for it to fail.

100m of 6mm² at 7.3mv/A/m is at max 16A so you will need 16mm² cable at 2.8mv/A/m to allow for volt drop.

I also have a degree in electrical and electronic engineering and sorry but what I learn in University does not help in working as an Electrician and it is what I have learnt to pass level 3 exams like the C&G 2391 which qualify me as an Electrician not the post level 3 taken in University and I would always call myself an Engineer never an Ex Engineer as I can never un-pass the exams. Retired maybe?

 

[BarryConvex]

LOL, I can tell the ex-engineer status is causing humour, understandably. Mechanical engineer that is, but with obligatory elec experience and an ability and willingness to learn and understand, that's why I'm asking.

OK, some background. We were advised to buy this 6mm cable at our first gig last spring by the on-site power guy who knew how far we would be from his generators. We weren't using the extra urn at the time and everything has worked since. The new urn puts us up to around 16A, hence going for 32 supply rather than straining a 16A.
V drop calculator here:
http://www.stealth316.com/2-wire-resistance.htm
tells me 5V drop at 16A and 10V at 32...?
It's quality Arctic Blue but we've never quite needed it's whole length so have been considering splitting it at 30m to give length options of 30m/70m/100m...

Regarding safety: Yes I have a duty of care, that's why I'm here on this forum. The question about a simple junction box was more about avoiding problems with RCDs on generators than avoiding cost. Since the Rubber Box stuff uses RCBOs I'm assuming problems were occurring elsewhere as electronicsuk said. Trouble is, I don't get to touch the generator, that's the onsite distro guys job.

Good point about the 3x 6gangs not being fused though. 3x single trailing sockets instead so fuses would be in 6gang plugs?

Moving on to safer options though. I appreciate that a £250 rubber box is the quick and safe answer but I have time to build something and saving £200 is relevant to me:

Brand new garage CU with 30mA RCD and 2x 16A MCBs for £25. (£31 for an IP65 unit but the 13A sockets are prone so the unit will be under a work surface anyway)
2x double sockets for about £3.
Already have offcut of the 6mm flex and a 32A conn for a trailing supply lead. Plenty of plywood, silicone and yacht varnish.
Lets say £35 total with a few misc items.
Who wouldn't want to save over £200 if it was legit/ safe/ practical?

Anything I put together will be PAT tested, as all my kit is. Is there really any reason why my suggestion isn't legit/safe?

Thanks for comments so far.

 

[BarryConvex]

Thanks ericmark, good info. You managed to post while I was typing my last post.

BTW not retired, just changed career (thrice!)(Time served, with lots of time with the maintenance guys)

Good to hear the generator has requirements too - as I said, that's out of our hands though.

100m of 6mm² at 7.3mv/A/m is at max 16A

Also good to hear, since we're only just at 16A. The urn is a temporary 2nd urn, our 1st being gas. Want to get a 2nd gas urn at some point which will bring us back down to 8-10A.

Every council safety officer has been happy with the 'grade' of the cable since it's always routed very carefully. ie, not through walkways or traffic. Hmmm, spec seems to go out of the window when in a field then?

They've also been happy with 13A sockets. Under heavy military canvas then hung under table top, under plastic box etc. They seem to be happy if you are aware of potential hazards and have addressed them, rather than spec.

All good info thanks. Any more one a self built distro box?

 

[NotHimAgain]

£35.00 that's good, but what about the £2000.00 for adequate professional indemnity and product liability insurance, and the costs of 'type testing' etc. to ensure any applicable standards have been met.

Then there is public liability insurance, etc, etc - I think £250.00 was quite cheap for something to be used at an event open to a litigious public don't you.

 

[ericmark]

Wiring Matters published by The Institution of Engineering and Technology Summer 09 Issue 31 has an article by Mark Coles on Cables for temporary electrical installations. In this he questions the use of Blue Arctic Cable and although I think he has gone a little too far he does make some good points and I would never use Blue Arctic Cable unless protected by a 30ma 40ms RCD to reg 415.1.1 and I would have thought the main supply cable should be of one of the two types I have shown or you need a 30ms RCD at the generator and if it trips tough.

Download Cables for temporary installations (570 k) and read then I am sure you will have loads more questions and we will be happy to discuss them with you.

I did check with Batt Cables as to use of Arctic grade, low temperature cable and it says

Standards: Generally to BS6500: Electric Cables. Flexible cords rated up to 300/500V, for use with appliances and equipment intended for domestic, office and similar environments

Applications: For use outdoors and where flexibility is required at sub zero temperatures. The cable remains flexible down to minus 20 degrees centigrade

This seems to in some ways contradict what Mark Coles says but if not working at sub zero temperatures is it really the best cable to use. Not sure what an insurance company would say?

 

[Spark123]

There is another British Standard which can be read in conjunction with BS7671 which covers this type of event:

BS 7909:2008 Code of practice for temporary electrical systems for entertainment and related purposes

Try your local library.

 

[electronicsuk]

OK, some background. We were advised to buy this 6mm cable at our first gig last spring by the on-site power guy who knew how far we would be from his generators. We weren't using the extra urn at the time and everything has worked since.

As you say, you weren't using the extra urn at the time. At 16A I would think you're just about on the limits of 6mmsq in terms of volt drop, although again that's only a rough guess. You should be looking for no more than 3% volt drop if you're running lighting as well as catering equipment, which I would guess you are.

If you stick with 16A connectors on the cable and assuming it does indeed comply at full current, then no problem. If you fit 32A connectors then you need to be sure the cable can support the full load, even if you don't plan to run it at that, as the nature of temporary installations lends itself to variability. You can't guarantee there will always be a 16A load at the other end.

The new urn puts us up to around 16A, hence going for 32 supply rather than straining a 16A.
V drop calculator here:
http://www.stealth316.com/2-wire-resistance.htm
tells me 5V drop at 16A and 10V at 32...?

I haven't tried that calculator, although it doesn't even list our metric cable sizes, so it isn't really applicable to us over here in the UK. In any case, 10v @32A is definitely more than 3% of 230v, so the volt drop is too high to run at 32A with your existing cable.

It's quality Arctic Blue but we've never quite needed it's whole length so have been considering splitting it at 30m to give length options of 30m/70m/100m...

Splitting it would make sense to save you the effort of reeling it all out for every event, if nothing else. Unfortunately it doesn't solve the issue of high volt drop when you need to use the entire 100m length.

Regarding safety: Yes I have a duty of care, that's why I'm here on this forum. The question about a simple junction box was more about avoiding problems with RCDs on generators than avoiding cost. Since the Rubber Box stuff uses RCBOs I'm assuming problems were occurring elsewhere as electronicsuk said. Trouble is, I don't get to touch the generator, that's the onsite distro guys job.

If the generators are set up by the company supplying them then the earthing arrangements should all be in order. I had assumed that the generator was yours.

Good point about the 3x 6gangs not being fused though. 3x single trailing sockets instead so fuses would be in 6gang plugs?

It's still no good, as I can't see how you'll fit cable with a CSA larger than 2.5mm^2 into the sockets, and that isn't rated to 32A.

Brand new garage CU with 30mA RCD and 2x 16A MCBs for £25. (£31 for an IP65 unit but the 13A sockets are prone so the unit will be under a work surface anyway)
2x double sockets for about £3.
Already have offcut of the 6mm flex and a 32A conn for a trailing supply lead. Plenty of plywood, silicone and yacht varnish.
Lets say £35 total with a few misc items.

Who wouldn't want to save over £200 if it was legit/ safe/ practical?

I'm not saying that you couldn't create a relatively safe form of distro that way, but it will look carp, and it unless you use a weatherproof CU, glands and sockets, I wouldn't consider it suitable for the environment it's going to be used in. I don't have my red book in front of me right now, but I'd be suprised if it meets all the requirements of sec. 711.

If you must consider making your own then it would be far better to use a suitably IP rated polycarbonate box, fit a weatherproof transparent hinged window and DIN rail to mount MCBs/RCBOs, and then mount weatherproof 13A sockets or 16A ceeforms onto the box. By the time you've gone to all that effort, it probably wont be worth saving £100, and you still have no guarantee that it's safe to use unless you have some method of testing what you've built.

Anything I put together will be PAT tested, as all my kit is. Is there really any reason why my suggestion isn't legit/safe?

PAT testing is better than nothing, but it doesn't guarantee correct operation of RCD, RCBOs, etc.

 

[BarryConvex]

£35.00 that's good, but what about the £2000.00 for adequate professional indemnity and product liability insurance, and the costs of 'type testing' etc.

Hehe, a relevant point well put. I, however am not mass producing a unit for sale to the public. I am striving to design and build a bespoke unit which is safe and 'fit for purpose'. I also have a PAT man who a) suggested this in the first place, and b) will check and test the unit and certify it under his name (and, presumably, insurance) if he is happy with it. If not, he will inform me what is wrong, he just doesn't want to sit down for an hour with me to design it, so I came here for help with the design.

In this he questions the use of Blue Arctic Cable

Although he doesn't justify his objection specifically I can't help assuming that he's referring back to the earlier bulk of the article which discusses, at length, potential damage to the cable and avoidance thereof. He even admits that the standard (BS 7909:2008) is "descriptive, more a code of practice" and then goes on to highlight the obvious H&S procedures which I follow regarding safe routing (away from public access, traffic areas, exits etc). Also, the spec states "Cables with armour protection are not usually necessary." It is, in fact, the voltage range for outdoor use which it falls short on (should be 450/700).

I don't really want to dwell on the cable since safety inspectors always check my cabling and routing and if I get a statement from a council official stating "Your setup is safe" what else am I supposed to do? I will raise this next time I am inspected though and get a definitive answer. If it is negative there is usually a cable hire option from the distro guys. I will be shortening it though since the only time we've used the whole length is when we've been supplied power from a household 13A socket! (minus the extra urn obviously)

So back to building a distro box.

I'm not saying that you couldn't create a relatively safe form of distro that way, but it will look carp

lol, you haven't seen the rest of my setup

it would be far better to use a suitably IP rated polycarbonate box

So it's this then: http://www.alertelectrical.com/Cons...t-3-way-IP65-Garage-Consumer-Unit-A286002.asp and swap the 6A MCB for a 16? It'll still save me £200, maybe you lot have £200 more spare than I do.

Honestly, walk around a 50,000 capacity festival with 1000's of stalls and tents with power and look at the average hook-up. I'm being 10 times more conscientious than 99.9% of them - and they all still get signed off by the council officials. It's nuts...

Thanks again.

 

[BarryConvex]

I'll definitely look into dropping down to 16A connectors.

So, the CU I suggested in the previous post, which has a 30mA RCD with 2x 16A MCBs and add a 2gang 13A socket to each 16A circuit? 2.5mm2 household cable internally? 6mm2 external supply cable?

 

[ericmark]

I did say thought he was going OTT but if you needed new cable thought you should be aware before buying.

As for sockets using 13A is protected means of course that all plugs are fused and no need to use MCB's to reduce max current that can be drawn you must consider if suitable in other ways. It is permitted to supply 13A sockets with a 32A supply but not 16A because the latter are not fused.

OK there are exceptions and there are round 15A sockets where the pins are also fuses but would not recommend that type.

711 and 740 are quite new regulations came in June 2008 and arctic cable rated Voltage: 300/500V but 740.521.1 Cables and cable management systems states

Cables shall have a minimum rated voltage of 450 / 750 V, except that, within amusement devices, cables and cords having a minimum rated voltage of 300 / 500 V may be used.

when there is time to correct things I would take a chance but if should an inspector reject it there would be a time problem to correct it then may be not worth the chance.

I would agree there are many who seem to get away with a load of sub-standard installations and one feels one is going OTT but I have also been where something has failed and everyone is going daft to try to get it passed before opening time.

As to PAT testing that does not really comply for what you are doing. The forms you need are available here again free down load so why not take a look.

 

[BarryConvex]

There won't be any 16Amp conns coming out of it so no issues with lack of fuse there.

I'm pretty clear on the cable situation now, thanks.

So a distro box as described would be an 'install' rather than and 'appliance' so it needs commissioning rather than PATing. Lots of friends in the building trade, is it something a site sparky could sign off?

Internal cables? I'm assuming I won't be using the 6mm arctic. 2 core twin and earth 2.5mm with extra earth sleeveing?