30 amp off a ringmain trick

Gritineye · Sep 11, 2012

Forgive me if this has been discussed before, but a friend told me this setup can be seen in use in the theatrical lighting world for those big ole Super Troopers, seems they where even available commercially.

Thought I would make up a set for use when welding away from home...may work better the right way up though..

Edit: Image has been removed by the OP in case anyone gets ideas, the reason can be clearly seen from the responses in the thread.
Play safe kids! :hug:

Paul. · Sep 11, 2012

That set up is extremely dangerous, if one of those plugs is removed while switched on there will be a live exposed pin,

Gritineye · Sep 11, 2012

Never thought of that Paul...

Project aborted..

inchpincher · Sep 11, 2012

I'm not much of a sparky but that doesn't add up in my head. First off it looks like a spur not a ring main (unless its the final loop on the ring and the return cable is in the trunking), secondly sure the twin plug set up doubles the amount of cable carrying current to the 30amp socket but what cable is used for the ring main? What else is drawing current off the ring?

Seems a bit hokey to me but I'm prepared to be enlightened... :whistle:

wheresmejumper · Sep 11, 2012

a double socket isnt rated anywhere near 30 amps.closer to 15!

Gritineye · Sep 11, 2012

IPincher, it is a proper ring main, all three sockets in ring, sparky installed.

the snooper · Sep 11, 2012

as you cant see the wiring its hard to say it could all be part of the ring and a ring main is 30 amp cable and you could also plug 2 total separate 13 amp appliances into those sockets so there is no difference load wise

wheresmejumper · Sep 11, 2012

the snooper said:
as you cant see the wiring its hard to say it could all be part of the ring and a ring main is 30 amp cable and you could also plug 2 total separate 13 amp appliances into those sockets so there is no difference load wise

no,double sockets can supply a max of 14 amps on one,6 on the other.

they get too hot if any more current goes through them

tigler · Sep 11, 2012

The main safety concern has already been mentioned. Ultimately, the ring main is protected by a suitably rated MCB, so it can't be overloaded. If no other load is connected whilst the 30 amp load is on I don't see why it wouldn't work but that live pin risk just makes it a no no !!

rtbcomp · Sep 11, 2012

How can a 13A socket be permitted to supply 14A, the plug will be fused 13A (won't it?)

tigler · Sep 11, 2012

wheresmejumper said:
no,double sockets can supply a max of 14 amps on one,6 on the other.

they get too hot if any more current goes through them

In practice that depends on the quality of the socket in my experience.

tigler · Sep 11, 2012

rtbcomp said:
How can a 13A socket be permitted to supply 14A, the plug will be fused 13A (won't it?)

To me it reads 'is capable of supplying 14 amps'.

wheresmejumper · Sep 11, 2012

yes but it has to be over specc'd for safety purposes

the snooper · Sep 11, 2012

just been looking this up and its not totally clear some sockets apparently have a rating stamped on the rear of 20 amps and others 13 but what we do know is they are designed to have a maximum of 13 amps go through any 1 socket.

i never even thought of this problem as most other people i would presume, if you have a 13amp plug you know is safe so you would expect the double to take 26 amps there should be a warning that this isnt the case

Gritineye · Sep 11, 2012

Good input chaps, funny how it makes you think about stuff you take for granted, I always would have thought one could pull 26 amps continuous off a double socket, most people would I imagine. If it gets hot, there is a loose connection, or a dodgy/cheap socket.

Suppose the plugs where put in separate single sockets, surely that would provide enough current?

Talking hypothetically now of course

wheresmejumper · Sep 11, 2012

yes that would be fine(hypothetically!),as the input terminals and interconnects are rated the same on single and double sockets

the snooper · Sep 11, 2012

Gritineye said:
Good input chaps, funny how it makes you think about stuff you take for granted, I always would have thought one could pull 26 amps continuous off a double socket, most people would I imagine. If it gets hot, there is a loose connection, or a dodgy/cheap socket.

Suppose the plugs where put in separate single sockets, surely that would provide enough current?

Talking hypothetically now of course

no not for your adapter the 30amp socket could still pull another 4amps more then two singles are designed for

Gritineye · Sep 11, 2012

I have been using that 30 amp socket with just a single plug on it for low amps welding work away from home, sticking a second plug on seemed a neat trick to allow higher amps welding, which it would to a point.

But the thought of that live second plug is way too scary for someone who would forget his head if it wasn't screwed on (so Mrs Gritineye says) so it just ain't worth the risk.

Fazerruss · Sep 11, 2012

Still hypothetically speaking you could actually make a contraption like that a safe device to use if one plug was removed. All you would need to do is fit a couple of 240v relays/contactors that disconect the circuit if either plug is out.

Gritineye · Sep 11, 2012

Just to continue the two plug theme for your amusement and brain training, this was how the motor was wired up on a lathe I bought off ebay...I kid you not!

Lack of any form of earthing whatever was interesting!

30 amp off a ringmain trick

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