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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> I have a three phase convertor, with a reference l https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1312976605 Message started by kennymce on Aug 10^th, 2011, 12:43pm

Title: I have a three phase convertor, with a reference l
Post by kennymce on Aug 10^th, 2011, 12:43pm

I have a three phase convertor, with a reference leg ( Neutral ) this is used as a reference leg to the phase one to allow a connection of around 230 volts which will enable the control circuits of a 3ph machine to run or the likes of heating elements and so on, my problem is that there is 140 volt to earth on this leg when you would expect to see 0 volts in normal electrical conditions.

Can i put in a transformer to bring a earth back into play and tie the neg or 0 volt leg of the secondary winding to ground to achieve the correct readings and safe electrical working conditions.

Because the "neutral leg " is connected internally i cant ground the leg coming out as it will short circuit the convertor.

Title: Re: I have a three phase convertor, with a reference l
Post by kennymce on Aug 10^th, 2011, 12:45pm

Sorry i am bit of a novice at this so any help would be gratefully received

Many thanks

Title: Re: I have a three phase convertor, with a reference l
Post by kennymce on Aug 10^th, 2011, 2:29pm

Maybe i could even tie the supply neutral Nie's supply to the secondary negative zero of the transformer

Sorry my terminology is very general.

An also to avoid any confusion i don't want to step down the voltage from 230 to any lower i just want to make my "neutral" line safe again so maybe i need some other device not a transformer.

Title: Re: I have a three phase convertor, with a reference l
Post by CWatters on Aug 10^th, 2011, 5:10pm

I'm no expert but with some converters one of the three output phases is directly connected to the input phase. Perhaps possible to use that phase and the incoming neutral for control circuits. Check with the manufacturer. You would need to be sure not to accidentally connect the incoming neutral to the outgoing "neutral".

For example this manufacturer makes a range of converters. Their smaller converter (sizes 1 to 3) appear to have a 0V neutral output but the larger ones (4-64) don't. On their larger converters if you measure between each phase and ground you get different results. For this manufacturer the L3 phase is connected to the input phase so can be used for controls etc.

See the paragraph "Three phase voltages and neutral"..

http://www.isomatic.co.uk/3phConverterSelection.htm

Title: Re: I have a three phase convertor, with a reference l
Post by kennymce on Aug 10^th, 2011, 8:24pm

Thanks for you're reply . Yes i have looked at all that info and have found the correct phase and incoming neutral however i don't have my meter home tonight to take a reading. ill try tomorrow.

Also thanks for the link. I am going to contact the company tomorrow to see if they can offer more advice.

cheers.