Ring Final question - not DIY

[SUNRAY]

I gave a hand this morning with a fuse box change.

100A fused SWA feed 6x 15A feeding small machines such as pillar drill, bench grinder etc.

One circuit is a ring final using 6mm² singles E2E resistance 0.16Ω [~53m from memory] on a 45A fuse, at each of the 42 accessory points is a 60A isolator with 2 sets of singles feeding 2 DSSO's, some of these are up to 0.06Ω [~20m].

I suggested breaking it exactly in half onto 2x 32A radials

What other ideas are there?

 

[EFLImpudence]

Good memory.

Splitting it as you say seems like a good idea.


What else do you want to achieve or what problems do you perceive?

 

[EFLImpudence]

Oh, why did you say 32A?

Presumably it is in conduit, you could have two 40A - assuming it is not technically compliant at the moment.

 

[SUNRAY]

Good memory.

For some reason I remember 1+1mm² is 36mΩ/m and divide down.

Splitting it as you say seems like a good idea.
What else do you want to achieve or what problems do you perceive?
Oh, why did you say 32A?

Presumably it is in conduit, you could have two 40A - assuming it is not technically compliant at the moment.

Yes it's in conduit in an engineering training workshop with 36 benches and a few other bits on this board. Been like it for years, apparently without any issues until a few days ago when an angle grinder cable got caught on a sharp edge and 'electrocuted' [according to the w/shop manager] a trainee. He dropped it and with the grinder still running it ran across the floor and cut through another cable without blowing the fuse.
The kneejerk reaction has been to replace the fusebox with a DB with RBCO's. All good by me.
We were told 6 x 15A for machines and a ring final so went equipped with C16's and a C32 Eaton RCBO's, I suggested the split into 2 as a simple improvement and by absolute chance have a brand new one in the car but the boss preferred to return tomorrow with a C45.

Somehow a single 45A ring feels wrong for the situation, I'm sure it's technically safe but just feels wrong.

TBH I'm surprised it's not equipped with 110.

 

[plugwash]

How big are the singles from the isolators to the sockets? still 6mm?

 

[EFLImpudence]

Somehow a single 45A ring feels wrong for the situation, I'm sure it's technically safe but just feels wrong.

I have no doubt it is safe, so I suppose it must be 'allowed'.

However, a 6mm² single in conduit has a CCC of 41A so with 45A OPD, is it technically compliant?

Perhaps that is why someone made it a ring - but why not just two 40A radials in the first place?

 

[SUNRAY]

The wires and accessories are in perfect working order, there is no doubt at all of the safety of the installation. I hadn't considered the CCC. It's actually 7/0.044" in trunking which is more like 7mm² but the boss is too young to be familiar with it and insists on calling it 6mil in fact he started calling it 10mil as it's that sort of size. It's been there too long to question the original installation, If I were to do that i'd start with the whole layout, this part of the workshop is basically 3 rooms formed by angle iron frames to support the gas, water, air and electric services, black, white and notice boards etc but they're actually run around the middle section shown red. The brown, orange and green show the run between the isolators and sockets for the outside benches, personally I'd have installed 2 rings around the 2 outer sections to avoid those long runs and have the isolator for each bench beside the bench just like the middle rows. It would have been easier and use a lot less wire.
But that's all lost in history.

 

[SUNRAY]

How big are the singles from the isolators to the sockets? still 6mm?

Yes it's all 6mm² - actually 7/0.044" however each spur feeds only one DSSO so by todays standards 2.5mm² would be permissable for at least 2/3 of the spurs.