Sparky question about power outlets

[deema]

Firstly, thanks for your help, I’m installing the interlocked power outlets around the new workshop, originally I used to use single phase and three phase (3p+N+E) 16 and 32A outlets depending on what machines were attached. However, in my last workshop I found that I was upgrading the single phase to 3 as I updated my machines. So, I’m proposing to do away with the single phase altogether and just install 16/32A three phase outlets. I intend to wire the single phase machines up with 3 phase plugs, rotating the phases used on grouped machines that could be used at the same time. Is there a good reason not to do this? I can’t think of anything in the old wiring regs that would prevent it.

I am a competent person capable of carrying out this task, if you are not a qualified electrician, or competent in electrics and know exactly what you are doing, ignore this thread and do not try to replicate anything I’m suggesting. The voltages involved will kill you if you get it wrong.

 

[Sideways]

The biggest hazard(?) may be of a person coming into contact with two live phases from different sockets and exposed to 415V. Much more dangerous than 240V. But that would be a double fault as they should never come into contact with one live, never mind two at the same time.

If you wire all sockets 3pn&e then use a 3p plug on the tool with only one phase and neutral wired, there's a small risk that the neutral could come loose inside the plug and make contact with a second phase. Thus applying 415v across the tool. This would be dangerous. It is a fault scenario that could happen only while your tools were plugged into a fully wired 3ph outlet in your shop or elsewhere.

If you designate some 3pn&e sockets for single phase use and wire only one of L1, L2, L3 in those sockets, you remove this hazard. You'd just have Live Neutral and Earth supplied through a plug/socket that is electrically safe to do that. Someone unaware could then plug in a 3 phase tool to one of these special sockets which would not start as it would see two "failed" phases. Shouldn't be dangerous. Just confusing and with the potential for error as there would be some fully wired sockets and you might forget which were which.

This is very non standard. I don't think it introduces a high risk to yourself or others but I feel like it does increase risk due to confusion. I can't think of any specific para in the regs that says you can't install it this way but It wouldn't fly in a business / commercial setting probably under "duty of care".

To make this more controlled / deliberate. Wire the fixed sockets all 3ph per standard. Wire the tools with blue 16A CE plugs appropriate to them. Then have a bunch of adapter leads with a part wired 3ph plug on one end and a blue 16A CE trailing socket on the other. Use of the temporary, well labelled adapter leads would reduce the likelihood of confusion or error ?

 

[deema]

The biggest hazard(?) may be of a person coming into contact with two live phases from different sockets and exposed to 415V. Much more dangerous than 240V. But that would be a double fault as they should never come into contact with one live, never mind two at the same time.

If you wire all sockets 3pn&e then use a 3p plug on the tool with only one phase and neutral wired, there's a small risk that the neutral could come loose inside the plug and make contact with a second phase. Thus applying 415v across the tool. This would be dangerous. It is a fault scenario that could happen only while your tools were plugged into a fully wired 3ph outlet in your shop or elsewhere.

If you designate some 3pn&e sockets for single phase use and wire only one of L1, L2, L3 in those sockets, you remove this hazard. You'd just have Live Neutral and Earth supplied through a plug/socket that is electrically safe to do that. Someone unaware could then plug in a 3 phase tool to one of these special sockets which would not start as it would see two "failed" phases. Shouldn't be dangerous. Just confusing and with the potential for error as there would be some fully wired sockets and you might forget which were which.

This is very non standard. I don't think it introduces a high risk to yourself or others but I feel like it does increase risk due to confusion. I can't think of any specific para in the regs that says you can't install it this way but It wouldn't fly in a business / commercial setting probably under "duty of care".

Thanks, it’s appreciated, I hadn't considered the neutral coming free. Wouldn't in the this circumstance where there are two lives and no neutral cause the RCD trip?

 

[Spectric]

I intend to wire the single phase machines up with 3 phase plugs, rotating the phases used on grouped machines that could be used at the same time.

This could be very dangerous, also it would not meet the regulations which basically stipulate best practice. You should never say never because of sod's law and what might seem very unlikely can happen even if you think that the probability is zero.

This situation would be made much worse once you add extension leads into the equation as now you could bring together single phase power tools on different phases.

You need to keep all single phase outlets on the same phase, using Blue connectors and with there own protective devices it is a big no no to use a single phase device plugged into a three phase socket, it is just not done.

The only solution that comes to mind is to use something like this where each socket has local protection

https://uk.rs-online.com/web/p/indu...VpoBQBh330wRdEAQYASABEgI3APD_BwE&gclsrc=aw.ds

or something like this where it plugs into a three phase socket and provides various supplies but again with local protection.

https://toolsidee.co.uk/product/hbm...MI8rKH6YaOigMVpoBQBh330wRdEAQYByABEgKBn_D_BwE

 

[Spectric]

Wouldn't in the this circumstance where there are two lives and no neutral cause the RCD trip?

A three phase RCD does not require the neutral in order to trip, just leakage from line to earth.

 

[deema]

@Spectric Brilliant thank you for your replies. Now, I’m just trying to clarify my understanding. I recall that you should balance the load in the phases, so, ordinarily I would have placed each single phase outlet in rotating phase. Just I was planning to with the single phase connectors into 3 phase. However, if I take your point about single phase units on different phases coming together, that would suggest all single phase connections should be through the same phase?

One or two machines, that are three phase have an ancillary single phase plugs on them for extractors etc, and checking, none have their own protection.

It’s really got me thinking.

This isn’t a commercial shop, and machines are permanently plugged in. That’s not a reason for it not to be correct.

 

[Spectric]

I recall that you should balance the load in the phases,

I would not apply that unless it was a large industrial site because when you think about houses these are spread across the phases to help balance out the grid so further down the chain at consumer level your loads are not going to upset the grid. A bigger issue with large industrial sites with inductive loads such as big motors is maintaining the phase relationship between current and voltage where it can lag so sometimes needing capacitance banks to bring it back.

One or two machines, that are three phase have an ancillary single phase plugs on them for extractors etc,

I can remember working on some large lathes some years back that must have been fairly old because they were really solid beast with large chucks and a removable bed section with equally ancient switchgear. They had worklights on them that had a built in transformer to take the 400 volt down to 230 volt yet all the switchgear coils were 400 volt.

Something not yet mentioned is your supply to the premises, is it a three phase TN-S where you get a DNO provided protective earth or a TN_C_S where the Neutral / protective earth is combined into just one conductor, ie PEN ?

 

[Inspector]

Not an electrician or a pretend one either.

What would it do to the resale value or the sale of the property if a house inspector found the non standard wiring? Same question for a buyer having to consider the cost of standardizing or your family getting it rectified to complete a sale if you have kicked the bucket (hope not soon) and are not around to do it? Would the resale value be better with both systems separate and intact?

Pete

 

[Spectric]

What would it do to the resale value or the sale of the property if a house inspector found the non standard wiring?

a surveyor would probably not even notice anything and it is often only when something happens such as a thermal event or someone gets injured that anyone will take a closer look and even then the outcome is often a tick box exercise as it is domestic and not a place of work. The only people who would take an interest are insurance companies looking for a get out if a claim is made.

 

[deema]

Not an electrician or a pretend one either.

What would it do to the resale value or the sale of the property if a house inspector found the non standard wiring? Same question for a buyer having to consider the cost of standardizing or your family getting it rectified to complete a sale if you have kicked the bucket (hope not soon) and are not around to do it? Would the resale value be better with both systems separate and intact?

Pete

Thanks for raising it, it’s a good question. The sockets regardless of what they are will be wired to the regs. It’s only the machines / plugs arrangement that is the discussion. The sockets will also be signed off by a third party as part of the building regs compliance I have to go through for the building. From a resale perspective, it will ‘fly through’ as it will be fully compliant.

I stripped the last workshop of all the interlocked sockets, they are blinking expensive to buy new. However, as I hope that this will be my last home they will stay in place, or if not, I will hopefully be too old to play any more in the workshop so it’s been built to be as multifunctional as possible……including being capable of very quickly converting to our retirement bungalow!

 

[deema]

Just for giggles, I found the following plug, something I’ve never seen before, a five pin 240V…….could it be that others have trod the path I was looking to go down? It’s a reputable brand! Does anyone know what is actually for? Never come across this type of plug before.

 

[Spectric]

Having male pins then it would be the load side and not the supply, it looks like it is aimed at fitting to some enclosure to supply power along with maybe control but never seen one or used one.

 

[HOJ]

I have a selection of 1 and 3 phase oultets in my shop, and as is a certain law, I find I need to plug into the most convienent one, so i have made my 3 phase sockets all 5 pin and use a "special" cable
to then be able to use them to connect to a single phase machine, I would call it a flexible arrangement, but then I do know what I'm doing, and no one else has any invlovement.

With regards the 5 pin plug, I recall Lewden made a metal, weatherproof 16A one, we used to use in the Quarries and Ship yards, may still do, been a while.