3 Phase - 4 or 5 pin plug ?

[Courier]

All our 3 phase socket outlets are for 3 phases and an earth.

Have just taken delivery of a 7.5 hp 3 phase cold water pressure washer (Nixon) but it has come with a 5 pin plug and has both an earth and a separate neutral as well as the 3 power cores , the earth is the heaviest core.

There is no fancy control system or 240 volt contactor, just a 3 position rotary Off / 1 / 2 switch.

Can I simply connect across the Neutral and Earth with a suitably heavy link or do I need to do anything else ?

 

[Netherfield]

Wouldn't Nixon's know the answer to that question.

 

[Courier]

Wouldn't Nixon's know the answer to that question.

Yes, but they go home at 17:00 and we have only just unwrapped it [emoji848]

 

[Tim G]

I would say no, you'll need a 5 pin socket. I'd guess the burner needs a neutral to work.

 

[Courier]

I would say no, you'll need a 5 pin socket. I'd guess the burner needs a neutral to work.

Cold water - no burner . Our last one was a hot / steam and that ran on a 4 pin supply .

 

[Tim G]

Cold water - no burner . Our last one was a hot / steam and that ran on a 4 pin supply .

Ha, yes, re read your first post and see it says cold washer!

 

[Courier]

i have always been pedantic about having a good earth, its always the first wire I fit on any equipment and I know that our neutral comes off the same point as the earth in the Bus Bar Box so I am at a loss as to the difference between 4 wire and 5 wire 3 phase other than aesthetics.

 

[Dave W]

Trace the cable inside the machine. Make sure the neutral actually goes somewhere.
Presume you've had the plug off and it's not just 4 core into a 5 pin plug

 

[the-mad-welder]

I think five pin for three phase is the norm now when installing so I would assume that most new machines would come as five pin if they have a plug fitted, even if there is nowt connected to the neural connection. My whole workshop is done as five pin but the majority of the machines have no neutral connected, just the ones with a work light normally.

 

[Courier]

The neutral only goes as far as a “N” terminal in the 3 position rotary switch enclosure and then to the switch itself. The Earth goes to an earth terminal in the switch enclosure then there is a typical 4 core (3 black and earth) from the switch enclosure to the motor terminal box.
A link within the switch enclosure from the earth to the neutral would ensure that were the neutral essential then its purpose would be covered .....

 

[Courier]

[QUOTE="Courier, post: 5480598, member:\]
A link within the switch enclosure from the earth to the neutral would ensure that were the neutral essential then its purpose would be covered .....[/QUOTE]

Or maybe a link within the 5 pin plug - or both, just to play safe.

 

[agrimax]

@milkloss or @defender. Think these folks are well up on 3 phase leccy,if they're about............

 

[Servac]

The earth conductor is'nt there for that purpose. If you have an RCD it will keep tripping if current passes down the earth.

 

[e3120]

If you're absolutely sure the neutral doesn't go anywhere and isn't used, then I'd be fitting a 4 pin plug (I guess you've only got 4 pin sockets anyway). What to do with the neutral wire on the power cable is a funny one. I might just nip it off in the plug, but technically it should be linked to earth - not for the reason you were (not unreasonably) thinking of, but because spare cores are supposed to be earthed.

In general I wouldn't recommend joining N & E - not only does it play havoc with RCDs, but it's just a bit of bodge that one day another bodge might conflict with. Best plan (not that I practice what I preach) is to migrate everything to 5 pin.

 

[solo]

I have Nixon 3phase hot washer and if I use 5 pin plug all works fine but if I have to use a 4 core extension lead it will work ok on cold but the burner won’t.

 

[Baker9]

I have Nixon 3phase hot washer and if I use 5 pin plug all works fine but if I have to use a 4 core extension lead it will work ok on cold but the burner won’t.

Burner is single phase and so needs the neutral, I am not a spark but that is my understanding.

 

[solo]

Burner is single phase and so needs the neutral, I am not a spark but that is my understanding.

All plugs are 5 pin and very rarely use extension so not an issue. Nixon sorted me out with that issue when it was new.

 

[Tomtrac]

I am not a sparky
My 3 phase is earth going down armer cable and screws to the metal outer off the plug then to frame off comressors welders etc and three live and a neutral very old systemn no plastic plugs the old type with screw ring on outside of plug
As above not a sparky just being using -wirnig plus on for over thirty years lol

 

[Pheasant Surprise]

i have always been pedantic about having a good earth, its always the first wire I fit on any equipment and I know that our neutral comes off the same point as the earth in the Bus Bar Box so I am at a loss as to the difference between 4 wire and 5 wire 3 phase other than aesthetics.

Some 3 phase loads are unbalanced (star connection) and/or have single or two phase consumers within the device or appliance, hence the need for a neutral for the return current.

A pure delta connected 3 phase load, does not require a neutral. But as said not all three phase appliances/devices are delta wired.

 

[milkloss]

You might not need a neutral and it’s just easier for Nixon to put a 5 core cable on the machine. Neutral at the machine end might well be connected to a dead end but might also be the neutral for a 240v coil on the contactor.

If it doesn’t do anything I’d be inclined to wrap it with earth tape both ends and bung it in the earth connection.