110v 32amp leads on a 2.5mm flex

[Thomo39]

What are peoples thoughts on these leads, my workplace have just pulled them out of service stating that the maximum current a 2.5 flex will pull is 25amp, these leads are 25m in length.

 

[EFLImpudence]

Not sure what you mean.
What are "32A leads on 2.5mm² flex"?

2.5mm² flex does have a maximum rating of 25A (27A for T&E).
The flex cannot pull current; that depends on the load.

 

[SUNRAY]

What are peoples thoughts on these leads, my workplace have just pulled them out of service stating that the maximum current a 2.5 flex will pull is 25amp, these leads are 25m in length.

I know exactly what question you are asking.
When I was involved in PAT testing I had a booklet which showed what was and what wasn't permissable. I didn't like it but I was expected to pass such leads but there was a length limit, it was either 14m or 9m. This is based on the expectation that 110V extension leads are used for tools and not for continuous loads such as lighting.
16A 25m leads will be 2.5mm².

 

[ericmark]

Depends on the supply, a 32 amp MCB will likely open before a 2.5 mm² lead melts, but a 3 kVA transformer with a 13 amp fuse or even a 10 amp trip, with 55 volt to earth will pass 10/55*230 = 41.8 amp before the 10 amp trip will open.

I would like to ban yellow bricks, they cause so many fires due to having overload only on the input.

 

[SUNRAY]

Depends on the supply, a 32 amp MCB will likely open before a 2.5 mm² lead melts, but a 3 kVA transformer with a 13 amp fuse or even a 10 amp trip, with 55 volt to earth will pass 10/55*230 = 41.8 amp before the 10 amp trip will open.

I would like to ban yellow bricks, they cause so many fires due to having overload only on the input.

They don't need banning, they just need to be built correctly.

As a subby, In a workshop we fitted out a fibreglass cabi, this sort of thing:

to be sited on a roadside. The electrics as fitted by the company electrician consisted of about 32A 2p RCBO, 6KVA 55-0-55 transformer and a 'domestic CU' with single pole MCB's to feed the plant and several yellow sockets. I mentioned they should be DP and was told to mind my own business.
Not satisfied I went to the boss who also didn't understand and had to demonstrate my concerns.

I demonstrated a plug with a short length of 1.5mm² yellow flex and shorted blue and gren/yellow on the end, I stood there with the manager and the electrician watching wires overheat and smoking. In that system the potentil secondary current is more like 120A on a circuit designed for 16A before any hint of a primary overload.

Electrician was told to change the CU to accomodate 2P MCB's and repair all the damaged wiring, but worse they had to 'do a recall' job and travel round doing the same thing in previous cabins installations

 

[ericmark]

I was referring to these the reset button typically 10 amp ratting, these typically have two pole MCB's on the output so in the main OK, it is the yellow brick which is the problem, as said around 42 amp to trip the reset, the secondary problem is heat tends to build up quickest in the plug or socket, so with a PAT test one can inspect and see the damage unless part of the lead is covered, these can mean the cable heats up at some point along its length rather than at the ends, and the damage is very hard to detect, until that is you get a short circuit, by which time too late.

Where I work one building was part stripped of all electrics, then it was found there were other problems, and it was stopped, all original electrics have been isolated, and where the in comers are we have some 16 and 32 amp sockets at 230/400 volt. It is mainly used as a store now, but some work is done in it, and nearly all power uses the bricks and 110 volt. Even the lights.

No hot work permitted as no fire alarm system working, the 110 volt is the major cause for concern, 230 volt with RCD protection would be far safer, only good point is only around 6 people at a time are working in the building, but this must be repeated many times around the country, barns etc. Not really a construction site so construction site rules don't cover.

 

[SUNRAY]

Yes I'm aware of your comments regarding the 'bricks' and totally agree. I've always had the same concerns and as I mentioned previously all they require is suitable secondary OCPD and they'd be fine.
My reply basically described a similar situation to the 'brick' with OCPD on primary but in the instance OCPD in one phase of the secondary. My demo was to short circut the unprotected half of the secondary (just as you calculate) and I deliberately chose the socket with most wire to give a little extra resistance, just to ensure it didnt trip the RCBO.

One aspect that many users of bricks are totally unaware of is they are only rated for intermittant tool use, some give a continuous rating (if the lable is still in place) which is typically 600-800VA for a 1.5KVA.

 

[ericmark]

Yes it makes me cringe when used for lighting, as load can be there for many hours.

 

[SUNRAY]

Yes it makes me cringe when used for lighting, as load can be there for many hours.

A few years ago I was asked to provide a couple of "street lights" and a PA system for an outdoor carol service. The organiser stated the previous supplier had provided 2 pairs of 500W flood lamps on 12ft poles (strapped to existing gate posts) and wished for the same. Their own maintenance guy always laid on the power from the house.

When I arrived there were festoons hanging on the hedge running along both sides of the area and the couple of 4 way sockets as promised with a yellow brick pluged into each to power the festoons.
I erected the lights and plugged a pair into each 4 way as arranged then set up the PA system. At that point I went indoors to use the toilet and found 2 extension leads entering the building via a window and plugged into a DSSO in the passage. both cables felt distinctly warm.

Back outside I checked the yellow bricks were running ******* hot, check yes they were, Checked the rating of the bulbs; 25W, plant hire label on festoons showed 25m and 50cm spacing , 2 festoons plugged into each brick. therefore each 1.5KVA intermittant rated transformer running at 2.5KW continuous, additionally I had another 1KW of flood lights running on each 4 way. The extension leads were of course 1.25mm² and the DSSO was theoretically supplying 7KW plus the PA and an electronic organ and a couple of desk lights.
I managed to put in another lead to another room in the house to supply the PA and one lamp post.

Nothing stopped working but the heat, smell and the loud sizzzzing sound for 5-6 hours from both transformers convinced me they should have failed.

Funny thing is when we were packing up the maintenance man brought is car in and sitting in the boot were 2 spare (as he described them) transformers.


Of course building sites are a different matter, usually the 10KVA units on big jobs but smaller jobs there tends to be 3.3KVA versions and multiple leads and splitters meandering around with untold worklights running for 12 hours a day and frequently the 40W flou's go off everytime someone starts a drill due to the volt drop.

 

[AdrianUK]

Yes it makes me cringe when used for lighting, as load can be there for many hours.

Yes... nobody EVER turns off site lighting!