3ph to Single Phase

[crystal ball]

Also why hire companies are doing well, a firm I do work for hire out all sorts but their best "seller" is a pressure washer on permanent hire, pays for itself in weeks, when it conks out they buy a new one and off it goes

 

[SimonH2]

Yes but 3 phase is slightly different and the phases are different pulse widths.

As previously mentioned, that is complete and utter rubbish. Unless you had some timing reference, then if I offered you one phase out fo the three, then there is zero chance you could tell me which phase it was, or whether it came from a 3 phase or single phase supply.

Easy to correct on a small motor by simply swapping two of the phase wires over, but on some of the big stuff I regularly worked upon - you checked the phase rotation and made sure the motor went the right way first off, because they were so difficult to change heavy cables over.

At a previous job, we got a couple of large (for us) water chiller units installed for office AC. We knew that the site had reverse rotation, so every install had to have two wired swapped somewhere. The manufacturer's engineer came to commission the units when they'd been connected - so it was a quick prod of the armature on each contactor and see which way the fans ran, or whether the compressor units "rattled" in a manner characteristic of that type, and swapping two wires round as needed. Turned out that of the 6 motors (3 fans, 3 compressors), one was reversed compared to the rest

If the current rating on both ends is the same and the supplies have a neutral (I suspect they do, but you should verify) I see no problem with making up a lead with a 3 phase plug and a single phase socket.

Neither do I

Leads with different current ratings at both ends are more dubious (though commonly constructed in practice).

Indeed. A socket with a lower current rating than the plug being an issue in terms of circuit protection.
A higher rating socket than plug might not be an issue - depends on situation. I've been thinking of exactly that - fitting a 32A plug on a welder so that where a 32A socket is available it can be "cranked up", but where a 32A socket isn't available then use a 16A or 13A socket and dial back the current accordingly.

You can't do anything DIY in a commercial premises.

Rubbish. What you can't do "legally" is anything you aren't competent to do - which has little to do with being "professional" or "DIY". After all, on here and other forums there are plenty of examples of supposedly "professional" work which is anything but.
And being pedantic, anything done in-house is DIY - the in-house person did it (DI) and it was him that did it (i.e. Y, yourself). Also, if he's being paid then he is a professional - i.e. is being paid to do something.

provided you have complied with all of the required directives in designing and assembling it, tested it properly and completed the declaration of conformity (which you will obviously be keeping available for at least 10 years) and marked it appropriately with UKCA or CE or both marks depending on where it is to be used.

Riiiight. So when you get a professional electrician in to make up an adapter lead, he'll do all that will he ? Err, I doubt it.

On the market = the thing exists in the UK/EU and can be used in a commercial activity.

Wrong, it does not mean that. The legislation you link to is clear in that :
"For the purposes of this Directive, the following definitions shall apply:
(1) ‘making available on the market’ means any supply of electrical equipment for distribution, consumption or use on the Union market in the course of a commercial activity, whether in return for payment or free of charge;"
Note the "supply of ...". If I make a (in this case) cable for my own use, then this is not a "supply of electrical equipment" and therefore it has not been placed on the market. It's more interesting if I (or the OP) get in a sparky to make one for me - and may depend on how the contract is worded.
It could be argued that if I say "I need a cable to do ...", the sparky goes off to the wholesalers for the bits, and comes back to me with a cable to do <something> then that sparky has placed the cable on the market - but I doubt many would be saying that it would be reasonable (assuming he used all appropriately marked components) to expect him to go through the full declaration of conformity malarky.
On the other hand, if I got the parts and employed the sparky on an hourly rate to assemble them for me - then there's no doubt (except perhaps in your mind) that nothing has been put on the market.

 

[RandomGrinch]

Just to add my two penny's worth!
I have built and tested mains and low voltage equipment, I have a background involving electric and electronic engineering.

Three phase scares me!
The risks involved for the unwary and un-competent are massive.

The fact that the OP is considering DIY work on three phase suggests that either 1). They are somewhat competent and maybe have unofficial experience, or 2). They have no comprehension of the risks involved.

If it is no 2). This worries me deeply and I should hope that the many replies to this interesting thread may lead to them questioning their competency to perform this task.

 

[JohnW2]

Three phase scares me! .... The risks involved for the unwary and un-competent are massive. .... The fact that the OP is considering DIY work on three phase suggests that either 1). They are somewhat competent and maybe have unofficial experience, or 2). They have no comprehension of the risks involved. If it is no 2). This worries me deeply ...

I wonder what it is that you regard as being so 'scarey' about 'three phases'? One phase of 230V is more than enough to prove fatal as the result of incompetent work.

My house has a 3-phase supply - should I be scared to go near the electrical installation?

I imagine that the OP is probably competent enough to do what he proposed in his OP. Most of the discussion had been about legalities and bureaucracy, not competence.

Kind Regards, John

 

[Notch7]

Rubbish. What you can't do "legally" is anything you aren't competent to do - which has little to do with being "professional" or "DIY". After all, on here and other forums there are plenty of examples of supposedly "professional" work which is anything but.
And being pedantic, anything done in-house is DIY - the in-house person did it (DI) and it was him that did it (i.e. Y, yourself). Also, if he's being paid then he is a professional - i.e. is being paid to do something

I once rewired my joinery factory -distribution board, SWA radials to 15 machines, lighting 40 HF 1800mm dbls and single phase supplies -the original electrics was in a hideous state, which had been butchered endlessly over the years.
I got a company in to to a fixed installation test afterwards -that was all I needed to satisfy the insurers (Im not recommending anybody does their own electrics, only commenting how there didnt seem to be any regs stopping me do it).

 

[Notch7]

I wonder what it is that you regard as being so 'scarey' about 'three phases'? One phase of 230V is more than enough to prove fatal as the result of incompetent work.

My house has a 3-phase supply - should I be scared to go near the electrical installation?

I imagine that the OP is probably competent enough to do what he proposed in his OP. Most of the discussion had been about legalities and bureaucracy, not competence.

Kind Regards, John

Ive wired in loads of 3 phase woodworking machines -they are pretty simple TBH. The skill is knowing how to terminate reasonable size SWA.

I must admit I was defeated by trying to wire up a star delta

 

[JohnW2]

Ive wired in loads of 3 phase woodworking machines -they are pretty simple TBH. The skill is knowing how to terminate reasonable size SWA. I must admit I was defeated by trying to wire up a star delta

As I implied, there is nothing magic or scary about 3-phase.

If one is wiring 3-phase loads, one has to have a little more knowledge than is needed to work with a single-phase supply, but the OP was not even suggesting that - he simply wants to connect single-phase loads to his 3-phase supply - which is what happens in every final circuit in my house.

Kind Regards, John

 

[SimonH2]

The fact that the OP is considering DIY work on three phase ...

Are they ?
As I understand it, they are proposing to do a DIY single phase cable that happens to have a plug on it that has two extra unused phase pins. Would we be having the same conversation if someone was contemplating buying a "blue plug", a "blue socket", and connecting them together with a piece of suitable 3 core cable ? The difficulty here is really no different once you accept that the same cable wired into E, N, and one of the 3 phases of a "red plug" is really no different.
As long as someone is competent to fit said BS4343 plugs and sockets then what's the problem ?

 

[RandomGrinch]

As I implied, there is nothing magic or scary about 3-phase.

If one is wiring 3-phase loads, one has to have a little more knowledge than is needed to work with a single-phase supply, but the OP was not even suggesting that - he simply wants to connect single-phase loads to his 3-phase supply - which is what happens in every final circuit in my house.

Kind Regards, John

I would much rather treat a subject as scarey; making sure I understood exactly what I was doing and what the consequences of failure were, rather than be complacent in a subject I may not truly understand.
As you say, to deal with 3 phase you need a little more knowledge than dealing with single phase. You undoubtedly have this knowledge and experience. Many others won't.

 

[SimonH2]

And in this specific situation, the extra knowledge is "connect the brown wire in the flex to just one of the pins marked L1, L2, and L3 in the red plug and leave the other two pins with nothing connected". There's nothing else to know - he's already ascertained that there is a neutral, and if there weren't then all that would happen* is the single phase equipment wouldn't work.

* And there's the be the risk that someone who didn't bother to unplug before "poking around" might find the internals of the connected equipment all live". But then, anyone who doesn't unplug before poking around can find internals of equipment that's live.

 

[JohnW2]

I would much rather treat a subject as scarey; making sure I understood exactly what I was doing and what the consequences of failure were, rather than be complacent in a subject I may not truly understand.

Fair enough - if you don't understand the relationship between 3-phase supplies and single-phase ones,then you're probably sensible to keep away from the former.

As you say, to deal with 3 phase you need a little more knowledge than dealing with single phase. ...

You've only mentioned part of what I said - I said that one needed that little bit more knowledge IF one was connecting 3-phase loads - bit that is NOT want the OP wants, or proposes, to do.

You undoubtedly have this knowledge and experience. Many others won't.

As above, I wouldn't need any additional knowledge to do what the OP wants to do.

Bear in mind that, in the UK (and probably most places), virtually every home has an electricity supply which is one phase of a 3-phase supply.

Kind Regards, John

 

[funinacup]

This is running away with itself a little it seems!

Think I agree that it will be fine to make up a lead, and it seems there's no hard and fast rule for which live to use, and given the loads we'll be putting through it I doubt it matters much.

Thanks all.

 

[winston1]

I have built and tested mains and low voltage equipment, I have a background involving electric and electronic engineering.

Mains is low voltage. Your background didn’t teach you that?

 

[RandomGrinch]

Mains is low voltage. Your background didn’t teach you that?

Sorry - Extra Low Voltage!

 

[Harry Bloomfield]

And in this specific situation, the extra knowledge is "connect the brown wire in the flex to just one of the pins marked L1, L2, and L3 in the red plug and leave the other two pins with nothing connected". There's nothing else to know - he's already ascertained that there is a neutral, and if there weren't then all that would happen* is the single phase equipment wouldn't work.

With the proviso that the OP ensures that all of his single phases are the same phase, if they are to be in close proximity.