Ring Main fed via Contactor

[MarkyofftheMark]

I have a 13amp spur, fed by a 2.5mm cable, protected by a 16amp RCBO , supplying a contactor, which in turn has a ring main coming off it; this has roughly 30 sockets on it, for an IT suite.

This is the the first time I have seen a Ring main wired like this; Is this up to regs and if so what are the benefits of wiring it this way?

Thanks in advance

Mark

 

[malcolmsanford]

What controls the contactor? and what is the rationale behind the contactor controlling the ring, times?

You have a sort of Lollipop ring, granted a strange lollipop ring but there is nothing wrong with it.

The cable sizing seems correct to the protection unless there are severe rating factors involved.

 

[MarkyofftheMark]

There are no controls and have no idea regarding the rationale behind this; the contactor is fed off a 13amp spur. Could this be a means of preventing nuisance tripping on the RCBO? as its feeding an IT suite, running a large amount of computers.

 

[Pete999]

I have a 13amp spur, fed by a 2.5mm cable, protected by a 16amp RCBO , supplying a contactor, which in turn has a ring main coming off it; this has roughly 30 sockets on it, for an IT suite.

This is the the first time I have seen a Ring main wired like this; Is this up to regs and if so what are the benefits of wiring it this way?

Thanks in advance

Mark

30 sockets all for IT usage, what is the total Earth Leakage? has it been measured? people are saying that it's OK, can I refer you to page 81 section 7.5 this section covers socket outlets for IT installations, there are some basic differences between normal Ring FCs and Radial FCs, in my opinion it,s non compliant for the situation it is intended, should the total earth leakage exceed that stated in section 7.5

 

[malcolmsanford]

Pete I'm assuming you are referring to OSG here mate and unfortunately I don't have that here with me.

This maybe an installation before the amendment 3 it maybe an installation that predates the 17th entirely, we don't really know. Perhaps the OP can enlighten us.

He has a lollipop ring and I was answering the question is the ring compliant to any edition and as I noted for the cable sizing and protection devices it does comply.

The IT side of it is something else and could have been there before the introduction of section 543 of the regs.

Also I agree 30 sockets on a radial is a poor design, but again it does not contravene any regulation unless we start to go into 134 but that is more workmanship than design

 

[DPG]

Is there an e-stop which drops the contactor out? Unlikely I suppose but I can't see why the need for the contactor. Daz

 

[cobrauk]

Have had IT rings switched via a isolation switch so they can turn all computers off from one point but never 30 sockets on a 16amp circuit I would have had a 32amp Rcbo radial feeding the contactor.

 

[Pete999]

Pete I'm assuming you are referring to OSG here mate and unfortunately I don't have that here with me.

This maybe an installation before the amendment 3 it maybe an installation that predates the 17th entirely, we don't really know. Perhaps the OP can enlighten us.

He has a lollipop ring and I was answering the question is the ring compliant to any edition and as I noted for the cable sizing and protection devices it does comply.

The IT side of it is something else and could have been there before the introduction of section 543 of the regs.

Also I agree 30 sockets on a radial is a poor design, but again it does not contravene any regulation unless we start to go into 134 but that is more workmanship than design

Not saying you are wrong mate, just my opinion

 

[Flanders]

As said could be used for a last man out switch , 30 sockets is a lot for one circuit if they are used for computers then I would of thought the earth leakage would be too high and the inrush current would be to high, but that said if all the sockets are not being used and there are 30 sockets and only one computer that is moved around the room then as Malcolm says nothing wrong with the circuit, saying that as a guidance we would put no more that 8 twin sockets for IT equipment on a 32 amp ring final

 

[davesparks]

I have a 13amp spur, fed by a 2.5mm cable, protected by a 16amp RCBO , supplying a contactor, which in turn has a ring main coming off it; this has roughly 30 sockets on it, for an IT suite.

This is the the first time I have seen a Ring main wired like this; Is this up to regs and if so what are the benefits of wiring it this way?

Thanks in advance

Mark

1 it's a ring final circuit not a ring main, there is a difference
2 are you sure the 13A spur is feeding the contactor and not just supplying the coil circuit?
3 it's no different to fitting an isolator into a ring final circuit

 

[MarkyofftheMark]

Thanks for all your feedback, and I'll do my best to address some of your points.
- The installation definitely predates the 17th edition. Probably 25-30 years old.
- no estop to cut it out.

Also, I understand what a Ring Final circuit is, but I do incorrectly refer to it as a Ring Main; seems like quite a few people do.
What is a Ring Main? Not even google can enlighten me on this.

 

[Andy78]

A ring main is a distribution system where the arrangement is that of a ring. A ring final circuit is a final circuit where the arrangement is that of a ring.

I have to admit I'm puzzled by what is even going on here. I would say it was most likely that the 13A feed is being used to energise the coil with the RFC runing through the switched contacts as Davesparks suggests. If it is supplying the incoming switched contacts with a RFC off the outgoing side, what is switching the contactor ? or is it N/C ?

 

[Darkwood]

A ring main is a distribution system where the arrangement is that of a ring. A ring final circuit is a final circuit where the arrangement is that of a ring.

I have to admit I'm puzzled by what is even going on here. I would say it was most likely that the 13A feed is being used to energise the coil with the RFC runing through the switched contacts as Davesparks suggests. If it is supplying the incoming switched contacts with a RFC off the outgoing side, what is switching the contactor ? or is it N/C ?

It could be doing both, feeding the poles L/N and looped live side to coil ...who knows without the OP's input.

 

[Andy78]

It could be doing both, feeding the poles L/N and looped live side to coil ...who knows without the OP's input.

True. Forgot to put that option. We also need to know how many poles the contactor has and how the RFC is arranged. It could be many things depending on how it is connected. A lollipop ring, a true ring, a ring off a ring, or even 2 radials.

 

[DPG]

I think you're going to have to give us the full details of the wiring. Sketch a diagram out otherwise we're guessing. Daz

 

[Darkwood]

TBH - its poorly design from start to finish, can only really see it working as a last man out switch option as it doesn't comply to any other system for student isolation/safety out there so must just be a master switch. The contactor TBH serves no purpose if this is the case because using a DP 20amp switch would have served exactly the same purpose so I suspect the coil is directly energised of the supply side but possibly through a key switch descretely located that the OP has missed otherwise I'll say it again 'What's the point in it?'

 

[malcolmsanford]

My old mate hasn't come out for a while



As OP said it could be 25+ yrs old. It may not have been a contactor controlling 30 odd sockets in a former life but the ignition switch for the Star Ship Enterprise.