2 PHASE supply to machine

[mike the sparky]

I'm carrying out an EICR to a machine shop ( they make machine guns!). One machine is a sciaky P282 hot riveter. This starts out as a 3 phase, neutral & earth set up at the DB; then terminates in a rotary isolator 30 metres away where it changes to what I assumed was a single phase supply. This single phase supply is supplied from the red and blue cables in the isolator. Another 20 metres away is a MEM switched isolator next to the machine. A check inside this confirms 400volts. The machine has a built in transformer but no wiring diagrams are available. To me it seems to be a 230 volt machine but the operators tell me that there have been no operating issues. Is there such a machine that is 400volt, 2 phase, no neutral or is this potentially dangerous

 

[Knobhead]

Well done lads, you’ve just won Tony’s codswallop award of the day!

Mike, by asking the question you have proved yourself incompetent for this work.

Sorry to be so brutal, but the truth is “you’re just not up to the job”.

 

[Lucien Nunes]

Ah, I didn't say anything about a single-phase system as the OP's supply system is 3-phase. He asked:

Is there such a machine that is 400volt, 2 phase

I replied that if it is connected how he described, it is a single-phase machine which explains why it only needs two circuit conductors to supply it and hence in this case no neutral.

OT: To make a real 2-phase supply from 3-phase, you need a Scott 'T' transformer.

Lucien

 

[Knobhead]

Depending on how you connect a Scott transformer you can get four phases + neutral.

A Le Blanc transformer does the same job but is even more complicated.

 

[Outspoken]

If I understand you correctly, the supply is taken from two of the three line conductors of a 3-phase supply, without a connection to neutral. This makes it a single-phase machine, not two-phase. It just happens to be 400V, therefore the necessary voltage is found between two line conductors, rather than line and neutral. The idea is that by working at 400V where this is available, the current rating is reduced without the complexity and cost of a three-phase machine. Others have mentioned welders, indeed my own portable single-phase welder is switchable between 230 and 400V. At the workshop, I have many 16A 3-phase supplies and it will run on one of those on its 400V setting. However when set to 230V it requires a 32A single-phase circuit.

Two-phase systems were used in the past, they have two phases and a neutral or even two phases and two neutrals, and give a rotating field in a motor much like a 3-phase supply but with different phase angles. Two phases out of a 3-phase supply are not the same thing.

Lucien

Absolutely WRONG.

Using two phases out of a three phase supply for a machine (which is not uncommon) is DUAL PHASE, or more correctly it is POLY-PHASE and not SINGLE PHASE. Please read the definitions in BS7671:2008.

All systems that use more than one phase, whether they use/require a neutral are Poly-phase (Multiple phase) systems, this is true whether they use 2/3/5/7 phases.

The UK or any other nation have never generated two phase services, but on occasion some 400V machines where supplied by two phases from the public supply being taken into a building, usually the third phase was used for lighting and single phase power.

This country have generated power in 3, 5 and 7 phases in the past (415V, 535V, 633V), however the overwhelming majority of 5 and 7 phase systems where generated by "in-house" power stations for heavy industry, such as steel works etc. I have personally only encountered one 7 phase system and that was in a cement works that had a lot of old 1960's machines that used 630V to reduce start-up currents on motors due to their sheer size. To my knowledge no such system of this type exist anymore, at least in the UK, but I will happily be corrected on this.

 

[Knobhead]

OS if you want to push things you can get 48 phases from 3 phase. Used for rectifiers.

Most large cogging mill motors would use Ward Leonard DC control.

 

[Lucien Nunes]

I never said it was a single phase supply or single phase system, honest guv! I only said this of the machine, so I'm not contradicting any definitions. If you had a 230-400V single-phase step-up transformer, you could power the machine from a 230V single-phase supply. If, instead you power it from two lines of a 3-phase supply, that does not suddenly make it a polyphase load, even though the supply is polyphase. I had thought that mentioning this would clarify how it could function without a neutral, but the logic might have got buried in the following dialogue!

AFAIK 2-phase was popularised by Westinghouse in the early days.

L

 

[mike the sparky]

Thanks to all for your replies. Thanks to Tony for his Codswallop Award. If I am correct, the reason for this forum is to discuss and help fellow electricians with their day to day work. All I have seen is who's got the biggest phase combination. As for my spelling, I will try and get my teacher pal to check each of my replys/replies?????? The reason for the post was to get further information on wiring of. Thanks to Darkwood, yes the EICR does finish at the isolator but surely a competent electrician would question something that was not the norm. In all aspects of life there is room for growth and learning. Nobody ever knows everything, apart from my wife! As long as the PUB MEMBERS are providing us mere mortals with this wonderful information I'm sure all will be well. You can go and have a chat about me in your club now! Hopefully \I can join you one day, as I am partial to a pint or 3.

 

[shanky887614]

it is reply for single as in single phase
or replies as in polyphase for more than one

 

[Knobhead]

Many machines will have a 415V 2Ph supply, not many will utilise the neutral. I just can’t understand why you are knocking yourself out over this?

In years to come you will find many supplies like this. Don’t worry about them. 95% of them would have been installed by someone that actually knows what they are doing.

 

[Darkwood]

Thanks to all for your replies. Thanks to Tony for his Codswallop Award. If I am correct, the reason for this forum is to discuss and help fellow electricians with their day to day work. All I have seen is who's got the biggest phase combination. As for my spelling, I will try and get my teacher pal to check each of my replys/replies?????? The reason for the post was to get further information on wiring of. Thanks to Darkwood, yes the EICR does finish at the isolator but surely a competent electrician would question something that was not the norm. In all aspects of life there is room for growth and learning. Nobody ever knows everything, apart from my wife! As long as the PUB MEMBERS are providing us mere mortals with this wonderful information I'm sure all will be well. You can go and have a chat about me in your club now! Hopefully \I can join you one day, as I am partial to a pint or 3.

Dont add the paranoid trophy to your collection here ... forum rules means we cant discuss other members behind their back well in a negative vein anyway and unless you see something obviously dangerous with the machine like exposed live parts etc then ensure your customer knows where your EICR starts and ends..... whoever connect the machine up will have the responsibility of ensuring the the machine is connected correctly and is safe to use.....

Don't dig the hole you are stood in too deep that you can't climb out

 

[SKY]

I have fitted quite a few 2 phase forklift truck chargers - the first one I ever did made me think for a while!

 

[GLENNSPARK]

Seen welders that a 400v 2 phase.

stick plant

 

[Knobhead]

Not just stick plant.