Ring main advice please

[SUNRAY]

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?

No I'm not saying that at all and I don't think its fair to make the comparison.
Generally there is no increase in current when a phase fails in a 3ph system, if there is its most likely to be a motor circuit and will be protected by an overload device which will trip fairly quickly.

Back to the point in hand, lets assume (always silly) that the circuit is running at its full load of 32A and one contact of the 4 pole system fails, this means one wire is carrying the all the current.
The wire is running at around 120% of its capacity.
Now the real world, the circuit is 2.5mm singles in conduit and 75x50 trunking in insulation and I think its fair to guess its half full, lets say 10 circuits. I make it that the wire is running at around 333% of its capacity, unless I'm reading the (16th) tables wrong.

 

[Spark123]

I still think it is a poor setup - like you say in theatres you often end up with large ceeforms for things like sound fed from radial circuits. Radial circuits are pretty simple to switch via a contactor.
The concept of using cables in parallel is from using large cables - pulling in say a 1000mm^2 cable around a building could be a PITA, you can use 2 off 500mm^2 cables as long as you take precautions i.e. ensuring both cables take half the load each. 2.5mm^2 doesn't strike me as very large!

Out of interest - is it wired via a relay from the bell circuit of the fire alarm or from the dry relay contacts in the fire alarm panel?

 

[ban-all-sheds]

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

Ahhh........

 

[SUNRAY]

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

Ahhh........

But the regs state a maximum length, which I recall to be only 1 or 2 metres, for a cable not protected by an upstream OCPD. There appears to be no reg for the maximum length of an unfused spur on a RFC.

Just another double standard?

 

[SUNRAY]

I still think it is a poor setup - like you say in theatres you often end up with large ceeforms for things like sound fed from radial circuits. Radial circuits are pretty simple to switch via a contactor.
The concept of using cables in parallel is from using large cables - pulling in say a 1000mm^2 cable around a building could be a PITA, you can use 2 off 500mm^2 cables as long as you take precautions i.e. ensuring both cables take half the load each. 2.5mm^2 doesn't strike me as very large!

Out of interest - is it wired via a relay from the bell circuit of the fire alarm or from the dry relay contacts in the fire alarm panel?

I don't see why RFC should be any more difficult to switch than a redial.

I realise why parallel conductors are there, I have assisted with the installation of 4x240mm armoured singles per phase feeding a buss bar and 2x4c 240mm feeding a chiller. they were both a big enough PITA. There is no limit on the size that can be used s far as I can see. In this instance it was all there and is not easy to change the cable, we believe there are 4 inaccessible elbows in the trunking.

It's wired back to the fire panel and I was informed it only works on the smoke detectors. Although I guess thats incorrect, thats what I'll say till I know any different.

 

[Spark123]

I don't see why you can't use a contactor to control a RFC, however to keep it simple I wouldn't use parallel 2.5mm T&E feeding the contactor. I'd use either 4 or 6mm T&E.
Easy way to see if it is just the smokes - open up a break glass and get the bells going and see if it trips it!

 

[SUNRAY]

I don't see why you can't use a contactor to control a RFC, however to keep it simple I wouldn't use parallel 2.5mm T&E feeding the contactor. I'd use either 4 or 6mm T&E.
Easy way to see if it is just the smokes - open up a break glass and get the bells going and see if it trips it!

Initially I had no doubts about the method I used to wire and control the exixsting circuit whereas I had serious doubts about the original method used. With the concerns now raised here I would have had no hesitation in changing to 6mm (in fact as I have plenty of 16mm I would use that for future proofing) but as mentioned before the existing cabling is in trunking with bends in sealed voids and no viable allternative route.

Personally I'm not at all concerned with what part of the fire alarm controls the circuit as its all existing and accepted by the fire service and licensing authority.

 

[SUNRAY]

All sorted. I had an on site meeting this morning with a manager from the maintenance company.

I remember some bits wrong:
It's not 2.5mm, its 4mm
There's 2 control circuits labeled 'alarm & E stop' & 'Guardian' not 3 separate ones.

The Guy from the maintenance company initially took the stance that the PIR was correct until I showed him the original 16A contactors that his company installed and old & new circuit diagrams drawn on an old envelope.

He viewed it as 2 rings so I moved the the legs of the parallel feed from the SFCU & contactor to din rail terminals in the enclosure, then to the contactor & SFCU. So now it's a proper parallel feed. He did the tests, passed and reconnected it. Labels are to be engraved and fitted at each end indicating the parallel feed.

We then looked at the other 5 RFC's:
Hall, Kitchen, 2 meeting rooms and Committee room/corridor all controlled by 2x16A contactors and the 'Alarm & E stop' signal.
He has now failed these (but left them in service).

The circuits are controlled by:
The fire alarm system, cutting out on smoke in that room and bells.
3 off E stop buttons under flip up covers.
The intruder alarm, cutting out when alarm is set.
A 'OFF-NORMAL-OVERRIDE' switch for each RFC which overrides intruder alarm and E stop.

As a result of the meeting I have been asked to:
Quote to spend a day there with him doing a thorough inspection to establish exactly whats there in order that drawings can be generated.
Quote to change them all to single contactor and to rewire the switch arrangement so the E stop is not overridden.
Attend another similar property with him to repeat the above.

It looks like there may be more work my way too. Should I say I kinda like this guy?

My Thanks to every one who has assisted with their posts, they have been really useful to me.

 

[SUNRAY]

Anyone remember this?

Guess what...


The hall was inspected last week [only 18 months late for a 10 year inspection] and all the same questions are being asked again

 

[securespark]

Ha, ha!

You couldn't make it up!

 

[SUNRAY]

Ha, ha!

You couldn't make it up!

I wish I was

 

[securespark]

Surely you just need to wave your paperwork under the nose of whoever is asking the questions?

When they see the original circuit design Vs the amended one, surely they'll be good with it?

 

[SUNRAY]

Surely you just need to wave your paperwork under the nose of whoever is asking the questions?

When they see the original circuit design Vs the amended one, surely they'll be good with it?

I have my notes from the time which covers 3 A4 pages of scribbles but I know there was more, perhaps on scraps/passed on.
The original electricians at new build and PIR have ceased trading [ I'd predict retirement as the boss in post #53 was older than me] so this is a whole new event. The hall has the PIR but it seems the other documentation created at the time cannot be found and I wonder if it was never passed to the hall, I know it was created as he asked me to double check it.

 

[securespark]

Oh poo......

Sounds like a bit of a bonce ache. I wish I could help more.

 

[SUNRAY]

Oh poo......

Sounds like a bit of a bonce ache. I wish I could help more.

Yes it's this sort of thing that really annoys me especially as labels were made and stuck to the DB, which by the sound of it have been removed. I've offered to meet on site to offer assistance, we'll have to see how it goes