heavy duty 1ph welder

[ban-all-sheds]

Also stepping back a bit, it's been stated that it's not allowed to fit a 16A (with local overcurrent protection) or 32A socket to a ring main. It could be argued that this is in fact one of those rules (like a lot of Part P) that has negative consequences.

1) That rule is nothing to do with Part P.

2) What are the negative consequences of "Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury"?

 

[SimonH2]

Actually, 433.1.5 does NOT say that only BS1363 devices may be supplied by a ring final. It says that they can, and specifically overrides the restrictions of 433.1.1 - allowing* a ring final wired in 2.5mm which is too small to meet the requirements of 433.1.1. Yes, I've now been able to look up what it actually says.
* But not universally

Saying that <something> is allowed, is not the same as saying that <anything else> is not allowed.

In this case it is, because it's an exception. 433.1.5 describes the exception to 433.1.1.

Taken together, what they say, in effect, is "All circuits shall comply with 433.1.1, but if you have a ring final circuit with this sort of cable and that sort of protective device and if the cable is installed in one of these ways and if when used as intended it's not likely to be overloaded anywhere for long periods then you may use it to supply BS 1363 accessories."

If you have a ring final which complies with 433.1.1 then you may use it to supply anything.

Which is somewhat different to your previous statement that "433.1.5 only allows BS 1363 accessories to be supplied by a ring final". I know where that statement came from, and agree that it's being pedantic to disagree.

So my interpretation is that if you downgraded the RCD supplying the circuit to 20A so that 433.1.1 was met for every conductor - then it would be legal to wire a 32A, or 16A with local overcurrent protection, socket to a ring final.

Absolutely, because then you would not need an exception from 433.1.1

But as you recognise, you would have thrown away the reason for having a ring in the first place, namely the ability to use 2.5mm² cable on a 32A breaker.

Yes, but it's a matter of deciding what's more useful. If running in a new circuit would be difficult/expensive/be cosmetically unacceptable/whatever then downgrading the ring may be more acceptable than trying to run the big welder on a 13A plug.

Not the best way since you'd be derating the whole ring, and would be liable to nuisance tripping with a large welder - but if the main distribution board is not located where it's easy to run an extra circuit, then it would be an option.

A better option, depending on the installation method for the cable and the range of MCBs available might be to turn it into a 25A radial.

I wasn't aware that anyone did 25A breakers - my (admittedly limited) experience suggests most ranges jump from 20 to 32.
If you really know your stuff then 25A as a rewireable fuse is easy to do - but then really easy for the user to 'upgrade' later when he first blows it.

 

[ban-all-sheds]

Which is somewhat different to your previous statement that "433.1.5 only allows BS 1363 accessories to be supplied by a ring final".

You don't think that it's actually the same as my previous statement, and that it would have been pedantic to the point of barking mad to have said something like

"433.1.5 only allows BS 1363 accessories to be supplied by a ring final which uses 433.1.5 to qualify as an exception to 433.1.1"

?

If you really know your stuff then 25A as a rewireable fuse is easy to do.

2.5mm² T/E is not rated highly enough for a 25A rewirable fuse. Or, at least, not a BS 3036 one, if there is such a thing. I guess if you were using a different type you could use the manufacturer's data on its fusing factor and time to determine if it would be OK, but then you're off-piste again.....

 

[ericmark]

Hi Ericmark,

You said....

In the older sets for example the BOC the iron core is racked in and out with an electric motor and if left in racked in mode often one can't switch them on without blowing the fuse. I have manually racked out the core many times.

</soundOfPennyDropping>

I've a BOC 185amp set, how do you manually rack the cores back in? Err, no reason, just curious </soundOfBreaker>.

Also, another thing to consider when calculating the cable required by duty cycle. Big welders pass quite a lot of current even when not welding.

Cheers

Pete

Sorry missed this. There was a motor on the 300A units and a chain drive to rack the core in and out. I had to manually turn the chain to get core out to be able to turn on without the trip going because of inrush. But it was not possible to manually set once switched on. There was a two button control to the motor and a window to show setting.

 

[Stoday]

Back to Basics...

you could have a 16A socket added to the ring main (with local breaker to prevent overload on the socket).

Yes, indeed you can.

The On-Site Guide Appendix 8 :

Spurs
...A non-fused spur feeds only one single or twin or multiple socket-outlet or one permanently connected equipment...

Permanently connected equipment
Permanently connected equipment is locally protected by a fuse complying with BS 1362 of a rating not exceeding 13 A or by a circuit breaker of rating not exceeding 16 A and is controlled by a switch...

The above implies that BAS's interpretation of 433.1.5 is incorrect and SimonH2's is correct.

Now, I have quoted from the blue edition of the OSG; I don't have the latest one. It would be helpful if someone could confirm that the note on spurs has not been changed. If there's been no change and given the opportunity to make the change with a new edition, it's reasonable to assume the interpretation is intended.

 

[ban-all-sheds]

Back to Basics...

you could have a 16A socket added to the ring main (with local breaker to prevent overload on the socket).

Yes, indeed you can.

The On-Site Guide Appendix 8 :

Spurs
...A non-fused spur feeds only one single or twin or multiple socket-outlet or one permanently connected equipment...

Do you not see the problem there?

The above implies that BAS's interpretation of 433.1.5 is incorrect and SimonH2's is correct.

Stoday - I know that it's hard for you, and that it actually runs counter to your basic outlook on life, and flatly contradicts what you believe is the right way to approach a collection of words on a page, but try to understand the importance of reading the words that are there and not imagining that there are other words present.

My "interpretation"?

There is no "interpretation" involved - 433.1.5 simply does not contain anything about 16A breakers.

 

[Stoday]

Do you not see the problem there?

Oops! Yes, I should have said:

Yes, indeed you can, provided you leave the socket out and connect the welder directly to a 16 A local breaker or a 13 A switchfuse. That'll save you a bob or two.

My "interpretation"?

There is no "interpretation" involved - 433.1.5 simply does not contain anything about 16A breakers.

I never said that 433.1.5 said anything about 16 A breakers. I said the OSG did.

433.1.5 says that if you have BS 1363 accessories you can supply them using a ring final circuit. It says nothing about what else may be connected using the ring.

You have assumed that it implies only BS 1363 accessories may be connected. That's your interpretation.

The On-Site Guide has a different interpretation insofar as it allows "one permanently connected equipment" to be connected to a spur.

It is you, BAS, who is reading words that arn't there. You are reading a non-existant "only".