MCB for a compressor

[JohnW2]

What are these plugs and sockets for? - Appliances requiring more than 13A?

Interesting questions. They are obviously used for loads requiring more than 13A, but I'm far from convinced that they are used only for loads requiring more than 13A. Certainly with 110V ones on building sites etc., they seem to be used for almost any load, even if well under 13A. Indeed, when I moved into my present house, all of the outdoor sockets were (230V) 16A ceeforms (several per circuit!) - I suspect that they were the most common 'weatherproof' ones in the days when they were installed.

Is your interpretation of the regs that, at least in some circumstances, one could have two or more 16A sockets on a circuit with a 32A OPD (assuming cable was OK for 32A)?

No. What would be the point of having 16A plugs/sockets if they can be plugged into 32A circuits.

The 'point' would obviously be that one could have more than one 16A load supplied by the same circuit. We seem to be back to the question of 'what is being protected?'. If the circuit's cable is adequately protected by a 32A OPD and if, as you and I seem to have agreed, the plug/socket, per se, probably don't need protection, then what is it that would not be adequately protected' by the 32A OPD?

Kind Regards, John

 

[JohnW2]

deleted - clicked quote rather than edit yet again!

 

[Risteard]

If the circuit's cable is adequately protected by a 32A OPD and if, as you and I seem to have agreed, the plug/socket, per se, probably don't need protection, then what is it that would not be adequately protected' by the 32A OPD?

Don't forget that fault protection will also be required for the flex coming out of the plug!

 

[JohnW2]

If the circuit's cable is adequately protected by a 32A OPD and if, as you and I seem to have agreed, the plug/socket, per se, probably don't need protection, then what is it that would not be adequately protected' by the 32A OPD?

Don't forget that fault protection will also be required for the flex coming out of the plug!

Sure, but I was including that with "the circuit's cable". Fault protection of that flex is not likely to be an issue (as previously discussed, surprisingly small cables get adequate fault protection from surprisingly large OPDs), although overload protection, if it were deemed to be required, could be more of a problem.

Kind Regards, John

 

[Risteard]

If the circuit's cable is adequately protected by a 32A OPD and if, as you and I seem to have agreed, the plug/socket, per se, probably don't need protection, then what is it that would not be adequately protected' by the 32A OPD?

Don't forget that fault protection will also be required for the flex coming out of the plug!

Sure, but I was including that with "the circuit's cable". Fault protection of that flex is not likely to be an issue (as previously discussed, surprisingly small cables get adequate fault protection from surprisingly large OPDs), although overload protection, if it were deemed to be required, could be more of a problem.

Kind Regards, John

Ask yourself why the need for a fuse in the plug with ring final circuits. This issue does not arise on 16A radials.

 

[JohnW2]

Ask yourself why the need for a fuse in the plug with ring final circuits. This issue does not arise on 16A radials.

Well, it wouldn't arise with a hypothetical 13A radial.

What you are saying/implying corresponds with common sense. However, I seem to be getting somewhat mixed messages in response to my question. It was, in fact, you who suggested that (although I have yet to find the 'chapter and verse') the regs allow for multiple 16A sockets on a circuit protected by a 20A OPD - admittedly a fair step from 32A but, nonetheless, more than 16A.

Kind Regards, John

 

[EFLImpudence]

Yes, but you would not put a 16A (or 32A) plug on an appliance that required less than 16A overcurrent protection, would you?

It is up to anyone to design what ever is safe.

 

[JohnW2]

Yes, but you would not put a 16A (or 32A) plug on an appliance that required less than 16A overcurrent protection, would you?

Well, given thatthere are no fuses in the plugs, it's obviously not a question of 'which plug', per se, but I assume that your statement implies that you would expect any 16A socket to be protected by a 16A OPD?

As for your question, as I said, I think the answer is almost certainly that some people would if you look around building sites (or my garden when I first acquired it!)....

Kind Regards, John

 

[ericmark]

This has nothing to do with the case in question but as far as 16A sockets in general then clearly far more 110 volt versions in UK than 230 volt versions so we have to look at 110 volt.

Using a 5kVA transformer is completely different to using a 3kVA brick. I have no issues with a 5kVA even when a 20A double pole MCB is used to supply two 16A sockets.

However with the 3kVA brick it is all too common to use a 12A thermal overload and a 13A fuse on incoming supply as the only overload device. One has to remember the output is 55-0-55 so a fault to earth is only 55 volt. So 12/55x230 = 50A. So with a standard commercial set-up it takes 50 amp line to earth on a 16A plug to open the standard overload device.

Against these facts using a 32A B type MCB kind of disappears into a minor breach of overload facts for a 16A socket. As one might expect use of 1.5 mm² cable and extension lead into extension lead has resulted many times with leads melting rather than overloads opening when a short circuit to earth happens. This has caused many fires.

Also use of 300W quartz halogen lights has also caused many fires and it is hard to show how many fires are due to quartz halogen lamps and how many due to 110 volt brick transformers.

However to my mind the use of 110 volt on building sites using 110 volt bricks is seriously flawed and the sooner either the rules about 110 volt on building sites or the use of non compliant bricks is outlawed is changed the better.

With RCD protection there is no need for 55-0-55 or 63-0-63 volt systems and there needs to be a change in the regulations may be the 3th amendment has changed the requirement?

But how can anyone be upset when some one as a temporary measure uses a 32A MCB when manufacturers are still allowing up to 50A on the same socket design before any trip operates.

 

[RF Lighting]

I don't understand what you're getting at. All systems will allow a current much higher than they are designed for to flow in the event of a fault to allow an OCPD to operate.

 

[ericmark]

My point is using commercial plug and play units one can have 50A continuous load on a 16A socket.

So having a 32A load is nothing.

 

[stillp]

With RCD protection there is no need for 55-0-55 or 63-0-63 volt systems

Are you sure of that Eric? Remember the most likely path to earth is via a human body, so someone has to have a potentially fatal shock before there is any chance of an RCD operating. There's also the risk of a muscular reaction causing a fall from height.
This was reviewed by a BSI panel in 2013 as part of the routine review of BS 4363:1998+A1:2013. Specification for distribution assemblies for reduced low voltage electricity supplies for construction and building sites, and there was general agreement that the need for 55-0-55 V systems should remain. I believe HSE had some statistics that prove UK practice to be safer than the rest of Europe's reliance on RCDs, but I no longer have access to those figures.

 

[RF Lighting]

Sorry I missed what you were getting at. I don't think you can use the poor design of a transformer as rationale for overloading all bs60309 outlets.

 

[ericmark]

There is a difference between shock and fire and there has to be a balance between the two.

The use of quartz halogen lamps on building sites makes it had to work out if a fire is as a result of using a brick or the inappropriate use of the appliance.

I have no problems with a 5kVA transformer with MCB's on the output. But I do with the yellow bricks. They don't comply and should be banned. The same should apply to any device which stops safety systems form working. Walk around any small building site and there are yellow bricks everywhere.

To my mind any site which requires a 63-0-63 volt supply should have a transformer with MCB's on the output supplied by the main contractor. But even the cable has the wrong colours. Green/yellow, Brown and Black should be the colours used there should not be a blue core in any yellow flex but every three core yellow flex I have found has a blue core even when our 110 volt system has not got a neutral.

 

[stillp]

You're right about the limited fault current resulting from the yellow bricks, but given the temporary nature of supplies on building sites it would be difficult to provide a reliably low fault loop impedance.