Daisy chaining very small loads.

[Tigercubrider]

I got a *******ing at work due to someone else daisy chaining onto a four way that I plugged in.
I agree that daisychaining is not good practice and I have a bunch of 8 ways specifically to avoid it but people do like to find a socket and use it.

HOWEVER
In the chain were two camera chargers (5w?) for DSLRs, one 3w LED light.
The “other” unplugged a 75w TV to plug into the second lead and then another 60w light into that.

All leads were PAT tested not so long ago.

Thoughts?
Our H&S people hate daisy chains with a vengance but imho there’s no or minimal risk with what was plugged in.

 

[JohnD]

Presumably the beginning of the chain had a UK plug with a 13Amp (or less) fuse in it?

The warnings about daisy chains are appropriate to other, more primitive countries that lack our wonderful fused plug.

 

[SUNRAY]

Presumably the beginning of the chain had a UK plug with a 13Amp (or less) fuse in it?

The warnings about daisy chains are appropriate to other, more primitive countries that lack our wonderful fused plug.

Which wonderfull plug it that, I can't imagine for one second you are thinking about the BS1363 type.

 

[SUNRAY]

I got a *******ing at work due to someone else daisy chaining onto a four way that I plugged in.
I agree that daisychaining is not good practice and I have a bunch of 8 ways specifically to avoid it but people do like to find a socket and use it.

HOWEVER
In the chain were two camera chargers (5w?) for DSLRs, one 3w LED light.
The “other” unplugged a 75w TV to plug into the second lead and then another 60w light into that.

All leads were PAT tested not so long ago.

Thoughts?
Our H&S people hate daisy chains with a vengance but imho there’s no or minimal risk with what was plugged in.

I do it all the time but like your observation it's very unusual to be managing heavy loads.
a lot of my useage is audio/video where a system may include lots of low power devices like CD, MD, Cassette players, sound/video mixer, radio microphones, desk light and so on. Typically the heaviest, of say 30 units, being the 40W desk light. AFAIC the biggest issue being the size of a dozen or more wallwarts. and not being able to fit them into typical 8/12/20way sockets.
However I'll always try to have the first 4 way taking the first set of 4ways to reduce the number of junctions in line. Even the cheap poundland leads are fine carrying 500W in multiple daisychained systems for a while.

When it comes to heating or stage lighting applications I'd like to say NO as loudly as possible.

One of the temporary supplies I did was a training session for 32 people (4 rows of 4 6ft gopak tables) and each needed 2 sockets for what were basically desktop calculators with 10VA or so wallwarts and the odd phone charger, I mostly used 4&6 way 2m leads, up to 5 per row of students and the 4 rows were plugged into the one 4way. I can't remember the final loading over the week long sessions but I'll bet it was peak at <500VA.

Would I cold hire kit to be installed like that? Would I suggest others to install a system like that? No way. Not unless I know their abilities to check it etc.
Have I encountered systems like that? Hell yes, I once walked into an office and instantly noted the unmiskakable aroma of warm PCV cable; 27 work stations in sets of 2 or 3 PC with CRT monitor per desk daisychained along the desks on a single plug.
They never turned them off due to the difficulty of getting them all back on again due to inrush.

 

[big-all]

just fit a 7amp fuse then no danger [or near to zero]whatsoever even with a further even loosely coiled lead as more than a 2000w load would often blow the fuse assuming plus 50% overload on top off 1610w would not blow the fuse in general but well within maximum designed load off plugs sockets and wire involved so quite safe

but just my opinion

 

[SUNRAY]

just fit a 7amp fuse then no danger [or near to zero]whatsoever even with a further even loosely coiled lead as more than a 2000w load would often blow the fuse assuming plus 50% overload on top off 1610w would not blow the fuse in general but well within maximum designed load off plugs sockets and wire involved so quite safe

but just my opinion

Yes it's somthing I regularly do, but usually with 2P MCB.

One PA job I did for years required 120m of cable, using a mix of 1.5mm² and mostly 2.5mm² I added an enclosure containing 6A 2P MCB and an RCD. A device that had been in use for many years. I had several with different size MCB's and different connectors.

 

[big-all]

Yes it's somthing I regularly do, but usually with 2P MCB.

One PA job I did for years required 120m of cable, using a mix of 1.5mm² and mostly 2.5mm² I added an enclosure containing 6A 2P MCB and an RCD. A device that had been in use for many years. I had several with different size MCB's and different connectors.

i always de-rate fuses to 20-35% less than machine value in the plug as in general a 70% value reduction on a carterage fuse even with a few seconds start up current perhaps 3 times will not blow the fuse so much safer over all

i do often get told you are protecting the cable and not the machine but i choose to reduce the levela belt and braces measure

 

[ericmark]

Daisy chaining 110 volt extensions can cause leads to melt should a fault occur. The problem is often the transformer only has an overload at the input, common to have a 10 amp thermal overload plus a 13 amp fuse, so 10 amp at 230 = 41.8 amp at 55 volt, so with a few 4 way adaptors the cable resistance can be such that a short line to earth can cause less than 41.8 amp to flow, so the 10 amp overload will not release, but the current is well over what 1.5 mm² can take without melting.

The cure is double pole MCB's on the 110 volt side, there is a danger if single pole used that people think a supply is dead when there is still 55 or 64 volt to earth (single and three phase voltages) so it needs to be double pole, there is often no RCD so an earth fault will not cause it to trip, so it is how the yellow brick is wired which is really the problem.

However as long as the leads are short, in the main accidents like a scaffold pole hitting a cable, will open the 10 amp overload before anything melts. The larger site transformers are not a problem, it is just the small bricks which have a problem.

So one sees site rules saying an extension must not be plugged into an extension due to the problems with 110 volt supplies.

Before we had RCD's on all sockets there was a problem again you could have an earth fault with a 230 volt lead which the fuse would not clear in time, so long extension leads would have RCD plugs to ensure they would disconnect with a fault within the time allowed, the use of RCD's on all sockets has removed this problem in the main, but extension leads which may be used on supplies which are not RCD protected still need RCD plugs to pass a PAT test.

This is the problem with PAT testing, it is done for the environment where the item is found, move the item and the PAT test may not be valid.

For a safety officer to make a rule which allows leads plugged into leads in one situation and not in another is clearly going to cause problems, so simple rule is don't do it ever.

I do see the problem, we expect a ring final to have an ELI of 1.39Ω but if the supply comes from a 16 amp MCB is could be double that to start with, so a 13 amp fuse was 2.42Ω before the 5% added, so if the socket is 2.87Ω due to being a 16 amp radial then the disconnection time at end of an extension can easy be exceeded, one reason for not having radials and keeping to ring finals many seem to miss.

 

[SUNRAY]

Daisy chaining 110 volt extensions can cause leads to melt should a fault occur. The problem is often the transformer only has an overload at the input, common to have a 10 amp thermal overload plus a 13 amp fuse, so 10 amp at 230 = 41.8 amp at 55 volt, so with a few 4 way adaptors the cable resistance can be such that a short line to earth can cause less than 41.8 amp to flow, so the 10 amp overload will not release, but the current is well over what 1.5 mm² can take without melting.

The cure is double pole MCB's on the 110 volt side, there is a danger if single pole used that people think a supply is dead when there is still 55 or 64 volt to earth (single and three phase voltages) so it needs to be double pole, there is often no RCD so an earth fault will not cause it to trip, so it is how the yellow brick is wired which is really the problem.

Indeed a big problem and frequently not understood by highly qualified electricians; my post in a previous thread 2 years ago, in this case fitted with single pole MCB on the secondary which would have been fine for a L-N overload/fault but useless for a N-E (excuse the incorrect term used) fault:

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

As a subby, In a workshop we fitted out a fibreglass cabin, this sort of thing:
View attachment 268982
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 found sourcing a split phase distribution unit to be a problem, often ended up with three phase instead with every third blank.

But once using 4 KVA or above they tended to have MCB's on the output. Only the yellow bricks seem to be a problem.

 

[plugwash]

imho there’s no or minimal risk with what was plugged in.

I agree.

The question is, was that by luck or judgement? did the "other person" do a mental calculation before plugging stuff in? did the other person have any concept of the differences between small loads and large ones? or did they just yolo their plug in without any thinking at all?

I certainly remember stories from the University where I work, of people making chains of extension leads to power a bunch of computers. Then some idiot comes along and plugs a heater into the end of the chain. And this was in an electrical engineering department for ****s sake. The people involved certainly should have known better.

Plug fuses are certainly better than nothing, but there unfortunately does appear to be a window of currents where the fuse won't blow quickly if at all but the heat is enough to cause accelerated degradation. And in any case one of the basic ideas in safety is to try and avoid single points of failure.

 

[SUNRAY]

I found sourcing a split phase distribution unit to be a problem, often ended up with three phase instead with every third blank.

But once using 4 KVA or above they tended to have MCB's on the output. Only the yellow bricks seem to be a problem.

One of the places I worked had a 5.3KVA 'yellow brick' (5300VA) with a 2pole C20A MCB but still only on the primary and yes it originally had a 1,25mm² flex and moulded 13A plug.
Generally most of the 4KVA and above transformers tend to be 3 phase, one of the 15KVA transformers I was expected to install containd a 3ph dis board full of 2P MCBs which if you think about it may make sense if there is 110V between phases, however there is a distinct error there.