Oxford RT250 wiring question...

[Robbo71]

Hi all,

I have an Oxford RT250 that has been used at home on lower settings on 240v for ages. Have now moved it to my mates workshop where it can be used on 3 phase. ( I think the welder is actually single phase 400v?)

I need to fit a plug (5 pin type - the socket is 3 phase earth and neutral)

I have bought the correct plug, just need to know what pin goes to '0' on my welder and what pin goes to '400' (or maybe 415 ? ) on my welder.

My welder has pins for earth, 0 , 230 , 400 , 415

I've searched the internet and this site but can't find any concrete info.

Thanks for any help,
Rob.

 

[AdrianH]

I would have said wire the 0 and 415 connections between any two phase connections.

If you went to neutral and a phase pin you would only have 240 volts.

Not a sparky, but how I understand it.

Adrian

http://www.mig-welding.co.uk/forum/threads/oxford-wiring.13762/

 

[Robbo71]

Thanks for the info. The plate is the same as this one. The cable is 2.5mm 3 core standard brown blue green.

The plug has earth,neutral, R1 , S2, T3.

So just use blue to R1, Brown to S2 and earth to earth, with blue to 0 and brown to 415 at the welder end?

 

[eSCHEn]

Fuse

 

[pedrobedro]

why is there foil beside live terminals....

It looks like gaffer tape used as insulation.

 

[Robbo71]

It was gaffa tape used as insulation - that's how it was wired when I got it (400 pin and 0 pin going to the 4 pin type plug) I wired up a new lead for 230v as I have't got 3 phase at home.

 

[Robbo71]

"So just use blue to R1, Brown to S2 and earth to earth, with blue to 0 and brown to 415 at the welder end?"

Can anyone confirm that this is correct ? Just want to feel safe when I switch it on

 

[AdrianH]

I guess no one really wants to say yes, just in case there is a fault some where.

But, if the machine was mine, I would do a few checks first with a multi-meter on resistance to make sure there is no connection between the 0 and 415 volt terminals to the earth on the welder, wire the blue to R1, Brown to S2 and earth to earth, with blue to 0 and brown to 415 at the welder end. Last check at the plug end with the meter. I would then switch on welder, making sure no shorts on the output. Plug in the welder to the 5 pin socket and switch on at the socket assuming there is a switch there.
Fingers crossed no breaker trips out, last check with the meter now on AC volts between the Oxford metal case and another earth point, pipe wok etc to make sure no voltage present, then even gingerly touch case make sure no tingle. All OK, crack on!

No I wont be held responsible

Adrian

 

[Robbo71]

what amperage is the 3 phase socket?
What CSA / core thickness is the flex you used?

The socket is 32amp (put in last year)

The cable I have is 3 core 2.5mm H07RN-F H07

 

[Robbo71]

The plate says it has a max duty cycle of 7.5 KVA , whether that means max draw I'm not sure.

The welder will get close to 160A on 240v before it blows the 13a fuse. I have some bigger cable in my garage if you think it would be safer?

 

[AdrianH]

Yes, but now do the calculation at 415 volts because that is what it is going to be used on.

7500 W /415 Volts is equal to 18.07 Amps which is within the cable capabilities if the initial cable spec is correct.

Say the worst case is the volts drops to 380 Volts, then 7500/380 = 19.7 Amps.

But I can never understand if it is meant to supply 250 Amps what would the output volts be, Open circuit volts is 50 Volts but wonder what it drops to at rated current.

If the max input is 7500 then this means the arc volts must drop to around 30 Volts, does this seem correct!

Adrian

 

[brightspark]

and if it was on 230v check the fuse size that run it . now its on 415 the fuse size will be reduced

 

[Robbo71]

On 230v it was using a standard 13a fuse/3pin plug. The 3 phase supply I'm sure is 32A but will double check with my mate next week. I'm assuming there is no provision for fitting different fuses without changing his installation? (It's currently just running a 3 phase compressor) which I don't want to do.

I'll probably fit the bigger cable. I have enough spare so it won't cost anything.

Thanks everyone for the help btw.