3 double sockets on a three phase circuit

[Lectrician]

A 4mm, 4 core SWA is run to 4 pole rotary isolator from a 32amp three phase MCB. From the isolator, three lives and three neutrals feed three double sockets bushed to the bottom of the isolator.

On an EICR report, a C2 has been identified for this circuit - "Three single phase accessories split from one three phase supply. The neutral conductor shall not have a cross sectional area of less than the line conductors on single phase circuits and a cross sectional area of adequate size for design current and not smaller than 16mm for copper and 25mm for aluminium"

Bearing in mind all the other defects have been identified and quoted with a reg number it deviates from, this observation has no regulation number quoted. Where the hell has that come from?

The neutral current will never be more than any one phase, and with three sockets pulling full load, neutral will obviously be zero. Ideally, you would have a small TP DB before the sockets, but TBH, I really cannot see anything wrong with what has been done at all.

Comments?

 

[ricicle]

Any engineer with a bit of savvy could work out for themselves that there are no issues rather than trying to make up a problem just because it's a little unusual.

 

[plugwash]

I've no idea what the guy is going on about regarding the cables.

There is an unrelated potential issue I see which is that there is very little legitimate reason for having a 32A circuit with one double socket on it. Double sockets are NOT designed to run with both sides fully loaded. Depending on the situate having a 32A supply terminated in one double socket seems like asking people to overload that socket.

 

[ricicle]

There is an unrelated potential issue I see which is that there is very little legitimate reason for having a 32A circuit with one double socket on it. Double sockets are NOT designed to run with both sides fully loaded. Depending on the situate having a 32A supply terminated in one double socket seems like asking people to overload that socket.

The non-competant will not have an any idea of the size of protective device, the same for the size of protective device on a ring circuit. There is nothing to stop them plugging 26A worth of load in a socket on those circuits either.

 

[JohnW2]

There is an unrelated potential issue I see which is that there is very little legitimate reason for having a 32A circuit with one double socket on it. Double sockets are NOT designed to run with both sides fully loaded. Depending on the situate having a 32A supply terminated in one double socket seems like asking people to overload that socket.

That's equally true of any double socket on any 32A ring or radial circuit. Are you sugegsting that the risk of a 26A load being applied to one double socket is greater because each of those radials has only one double socket?

In passing, a B20 MCB would allow 26A to flow for at least an hour.

Kind Regards, John

 

[Lectrician]

The same guy as also done a code C2 for one double socket which is bushed to the side of the fuseboard and spurred from a B32 MCB feeding a ring. Absolutely nothing wrong with this, and in fact, if it was the only socket on the circuit and on still on a B32 with 2.5mm, you could still argue it is fine. That one always starts the arguments going

Another one which is not ideal is a 10mm XLPE SWA as a clipped direct submain on a C63 MCB - Ideally it would be a larger cable or smaller MCB in most peoples eyes, but the cable is rated to something like 70 ish amps clipped direct. Perhaps ambient temp needs to be taken into consideration for loft void, need to confirm later.

 

[JohnW2]

The same guy as also done a code C2 for one double socket which is bushed to the side of the fuseboard and spurred from a B32 MCB feeding a ring. Absolutely nothing wrong with this, and in fact, if it was the only socket on the circuit and on still on a B32 with 2.5mm, you could still argue it is fine. That one always starts the arguments going

I don't see why anyone should argue Would they also argue about a 2.5mm² unfused spur to one socket which originated at the B32 of a ring final?

Kind Regards, John

 

[plugwash]

My first question on seeing something like this would be "why did someone use a 32A three phase circuit just to supply a cluster of three double sockets?" I see three explanations.

1: the circuit already existed and was re-purposed.
2: they needed sockets on different phases for some reason.
3: they needed a lot of power in one place either to supply a large cluster of loads or because they had reached the limit of where they could take the permanent cabling and intended to continue in temporary cabling.

In scenario 1 or 2 double sockets would be acceptable, in scenario 3 IMO they wouldn't.

 

[JohnW2]

My first question on seeing something like this would be "why did someone use a 32A three phase circuit just to supply a cluster of three double sockets?" I see three explanations.
1: the circuit already existed and was re-purposed.
2: they needed sockets on different phases for some reason.
3: they needed a lot of power in one place either to supply a large cluster of loads or because they had reached the limit of where they could take the permanent cabling and intended to continue in temporary cabling.
In scenario 1 or 2 double sockets would be acceptable, in scenario 3 IMO they wouldn't.

Fair enough. Would you be happier if they added one or more additional sockets to each of the radials? If so, how would you guarantee that people would plug there loads into different sockets, rather than two into each double socket (the same issue as with any sockets circuit, really)? Would you perhps be happier with single sockets, rather than doubles?

The only real way to eliminate this problem (which is a totally general one) would be to either eliminate double sockets or else to force manufacturers (presumably by a change to BS1363) to produce double sockets which are capable of coping with continuous 2 x 13A loads.

Kind Regards, John

 

[Spark123]

There's something I remember about reduced sized neutrals not being allowed for use where there are harmonics present but I can't quote the reg.
However as it is the same size I don't see where that is going.

XPLE is rated up to 90 deg C so the current carrying capacity (85A/73A 1p/3p clipped direct) is only applicable if all terminations are rated up to 90 deg C also too.
For 70 deg C terminations the rating for normal SWA is 67/58A 1p/3p is a better one to use.

Is the EFLI in spec? I was tearing my hair out when they lowered the figures 16th/17th edn as I had one that passed with the old but not with the new!

 

[ricicle]

In theory, if the circuit is protected by a device where all lines are isolated at the same time ie a TP mcb then then you would only need one Neutral from the TP isolator looped between the sockets (same size as line conductors and assuming no third harmonics created by anything plugged into the sockets)

 

[SimonH2]

My first question on seeing something like this would be "why did someone use a 32A three phase circuit just to supply a cluster of three double sockets?" I see three explanations.

1: the circuit already existed and was re-purposed.

That's the one I'd assume. Seems quite reasonable to me - apart from the (not uncommon in larger sites anyway) issue of having 415V between sockets.

In theory, if the circuit is protected by a device where all lines are isolated at the same time ie a TP mcb then then you would only need one Neutral from the TP isolator looped between the sockets (same size as line conductors and assuming no third harmonics created by anything plugged into the sockets)

Suppose the circuit fed a small 3P distribution board - same size upstream breaker, same size cable, would there be any discussion of that normally ? I think you'd be really pushing it with just 3x double cockets to get loads that would overload the neutral - they'd have to be really, really bad loads.


Sounds to me like the guy producing these faults is either a numpty, or is looking for work.

 

[Astra99]

Sounds very much like a "jobsworth" who has done the half-day course and got a certificate to say he is a H&S inspector! Clearly he knows Sierra-Foxtrot-Alpha when it comes to electrical installation methods.

 

[JohnW2]

Sounds very much like a "jobsworth" who has done the half-day course and got a certificate to say he is a H&S inspector! Clearly he knows Sierra-Foxtrot-Alpha when it comes to electrical installation methods.

Isn't it a lot 'worse' than you suggest? - a briefly trained H&S inspector wouldn't be doing EICRs, would he?

Kind Regards, John

 

[mfarrow]

They've interpreted or mis-remembered 524.2 completely wrongly, which isn't easy.

Basically that sub-set of regulations says that the neutral must be the same as the line if the line is less than 16mm^2, but can be reduced if above that. If you have triplen harmonics though, you might need a bigger neutral than the line. There would be a lot of harmonics though to need 16mm^2 as suggested.