Ring main advice please

[SUNRAY]

2.5 is rated somewhat lower than 32A therefore should not be on a 32A supply which I agree with!

It should not be used to carry a load of 32A.

Good words!

 

[JohnD]

there are thousands of similar circuits in use across the land, are they all wrong?

If they're a ring taken off another ring, then, yes.

If you wanted to do it that way, you could have broken the old ring at two points and enlarged it into one big ring.

Or you could have had a 13A fused spur off the old ring with multiple outlets on it but this would be very limited.

 

[maltaron]

If there are so many "interpretations" of the regs they should be re-written to be less ambiguous, preferably by people who are at the sharp end of the profession.

 

[JohnD]

the people at the sharp end are usually far too busy doing the work to go to commitees and write documents.

 

[SUNRAY]

A long time ago i used to do electrical work in a licenced theatre

Now I am just a householder

I would certainly have put a submain to the stage area, and I would probably have run it at inaccessible height, like the stage lighting supply and controls cables. With a small CU feeding your stage outlets, and if you want, some EPO buttons and a contactor at the stage end. I would have had the stage CU where it was visible and accessible to the stage manager for RCD and contactor resetting but not easily interfered with by others. You could take working lights off the stage CU as well.

If there was to be a ring, it would only start at the stage area. However I would probably not use a ring as I would not want sockets across the front of the stage. There would be no sockets taken off the submain. There would be no sockets in the stage area fed from other circuits.

BTW I would also have preferred different coloured, or identified, sockets on the stage circuit to reduce the risk of confusion with auditorium sockets when a circuit was isolated for maintenance.

All very much understood, real theatres have significantly differing requirements to any other environment I can think of, my experience of theatres (other than the standard housekeeping services) is to have as much power available as possible on large ceeforms, then a portable CU can be plugged in to create whatever else is required for the situation.

This is just a village hall, not a full time theatre and the tyical use of these sockets is the disco or the keep fit CD player. In fact the regular disco users have sussed that they use the auditorium sockets as they are not controlled!

 

[SUNRAY]

there are thousands of similar circuits in use across the land, are they all wrong?

If they're a ring taken off another ring, then, yes.

If you wanted to do it that way, you could have broken the old ring at two points and enlarged it into one big ring.

Or you could have had a 13A fused spur off the old ring with multiple outlets on it but this would be very limited.

No its usually a 32A MCB, 4/6mm cable , 30/45A isolator beside the door to a room, then a ring. For example a presentation room or classroom so all the AV kit, blinds aircon etc is all killed when the room is not in use.

The topic is only one ring and the way the contactor(s) control it.

 

[ColJack]

ok, you've convinced me..

what I saw and interpreted it as from the original post ( and what the guy doing the PIR did as well by the sounds of it ) was that you had one ring that was switched by a contactor where the legs of the ring went through seperate contacts..
now you have in effect one ring supplying the contactor and another off it's output.. effectively a figure 8.. which we're told is a bad thing..

 

[ColJack]

Which regulation, i.e. xxx.y.z makes a 2.5mm² cable on a 32A breaker unacceptable?

that would be the one you kept beating someone over the head with in another long winded argument..

433.1.1 The operating characteristics of a device protecting a conductor against overload shall satisfy the following conditions:

(i) The rated current or current setting of the protective device (In) is not less than the design current (Ib) of the circuit, and

(ii) the rated current or current setting of the protective device (In) does not exceed the lowest of the current carrying capacities (Iz) of any of the conductors of the circuit, and

(iii) the current (I2) causing effective operation of the protective device does not exceed 1.45 times the lowest of the current carrying capacities (Iz) of any of the conductors of the circuit.

or Ib<=In<=Iz

it fails because in this instance In ( 32A ) > Iz ( 27A max clipped direct )

although the point I think you were making is that with the contactor open there is no load on it at all so it shouldn't be a problem.. but the regulation says otherwise..

 

[ban-all-sheds]

Is it a figure of 8, or is it a ring originating at a contactor which is supplied by a parallel circuit?

And anyway - I don't see anything wrong with a 4P contactor being used to break both legs of a ring. Are there actually any regulations against it?

Or is there a regulation which says "Circuit designs which baffle hard-of-thinking numbnuts with no imagination or powers of original thought when they carry out PIRs shall not be used"?

 

[SUNRAY]

Is it a figure of 8, or is it a ring originating at a contactor which is supplied by a parallel circuit?

If it was a 4or6mm instead of the parallel 2.5mm there would not be a question. Maybe a label informing of the parallel feed should rectify this.

And anyway - I don't see anything wrong with a 4P contactor being used to break both legs of a ring. Are there actually any regulations against it?

I think it could be described as fed at 2 points and a faulty contact out of 4 will result in one leg taking all the load, as opposed to to zero current if 1 out of 2 contacts fail.

Or is there a regulation which says "Circuit designs which baffle hard-of-thinking numbnuts with no imagination or powers of original thought when they carry out PIRs shall not be used"?

No its not a reg, its an advisory appendix

 

[plugwash]

If they are the only options I would consider paralell conductors feeding a contactor feeding a ring a better option than a four pole contactor breaking both sides of the ring for a couple of reasons

1: it's less bad (though still bad and there should IMO still be warnings) if some numpty puts sockets in the feed legs
2: with isolating both sides of the ring seperately a failed contactor could lead to a broken ring

 

[ban-all-sheds]

it fails because in this instance In ( 32A ) > Iz ( 27A max clipped direct )

So what's the situation with unfused 2.5mm² spurs from ring finals?

 

[ban-all-sheds]

I think it could be described as fed at 2 points and a faulty contact out of 4 will result in one leg taking all the load, as opposed to to zero current if 1 out of 2 contacts fail.

Is there the same concern, to the extent of saying "it could go wrong, so you mustn't use it", with 3- or 4-pole switches, contactors, MCBs, RCDs etc used in 3-phase circuits, where incomplete making/breaking of the circuit could cause problems?

 

[ban-all-sheds]

1: it's less bad (though still bad and there should IMO still be warnings) if some numpty puts sockets in the feed legs

To what extent should a designer be constrained by concerns over what incompetent and ignorant people, over whom he has no control, might do in the future?

 

[SUNRAY]

it fails because in this instance In ( 32A ) > Iz ( 27A max clipped direct )

So what's the situation with unfused 2.5mm² spurs from ring finals?

One of my thoughs too, although in theory the max load on the spur is 26A (2x13A plug tops).