Small industrial unit, advice on pricing

[malcolmsanford]

might want emergency stops as well

Though each machine should have this, running the circuit in a ring is an advantage if you wanted to use emergency stops. Ring would utilise 1 or 2 stops in various positions, individual circuits as in the 12 sockets would require 12 stops, but you would not do this and rely on the machines emergency stop system.

 

[davelerave]

Also don't know if I would go with the small radials and RCBO's it means a lot of ways taken up in the board. I would just run 2x 4mm 32a radials or 2x 2.5 rings.
For DBs I always find Wylex to be a happy medium for price and they are OK to install, Merlin Gerin (Now schneider) are probably nicest.

Like I say depending on how awkward it is, I would run trunking around and do tube down to points, it looks better than tray and swa in small workshops and is nearly indestructable. Will also save a fair amount on cable costs and it can be quite time consuming to get nice grouping of cables on tray if theres lots of little'uns.

ya-you don't need a load of rcbo's for 13amp sockets-but 1 ring risks overload and nuisance

 

[davelerave]

Though each machine should have this, running the circuit in a ring is an advantage if you wanted to use emergency stops. Ring would utilise 1 or 2 stops in various positions, individual circuits as in the 12 sockets would require 12 stops, but you would not do this and rely on the machines emergency stop system.

i waas thinking of a 3-pole n/o contactor in DB and stops -rather than stops for each machine

 

[malcolmsanford]

i waas thinking of a 3-pole n/o contactor in DB and stops -rather than stops for each machine

So you would run your 12 radial circuits via a contactor?

 

[davelerave]

prob the lot if i was fitting it- SP and 3P -excluding lights


depends on the rules?

 

[malcolmsanford]

What I think your saying is that you would put the incoming tails through a contactor, that is assuming that the DB is a dedicated board for power, there is no evidence of that, in fact as it seems to be a small industrial unit the chances are that is is a combined board including lights

Agree if it is a designated board just for the 3 phase sockets, it may pay you to wire the tails through a contactor, only down side to that is you limit what can be added to the board at a later date.

Also you would need a far larger capacity contactor that one just feeding a Ring Main to the 3 phase sockets.

Also the client may not take too kindly to the emrgency stop being activated, that also kills the 13amp sockets if they are feeding an office.

Also just as a note the contactor would have to a 4 pole as emergency switching needs to isolate all LIVE conductors.

 

[davelerave]

What I think your saying is that you would put the incoming tails through a contactor, that is assuming that the DB is a dedicated board for power, there is no evidence of that, in fact as it seems to be a small industrial unit the chances are that is is a combined board including lights

Agree if it is a designated board just for the 3 phase sockets, it may pay you to wire the tails through a contactor, only down side to that is you limit what can be added to the board at a later date.

Also you would need a far larger capacity contactor that one just feeding a Ring Main to the 3 phase sockets.

Also the client may not take too kindly to the emrgency stop being activated, that also kills the 13amp sockets if they are feeding an office.

Also just as a note the contactor would have to a 4 pole as emergency switching needs to isolate all LIVE conductors.

i've seen it done on MG boards where i work

it's easy to feed part of a sub-board through a contactor (and exclude lights and IT equipment obviously)

not familair with UK rules but i wouldbn't be using a 4-pole contactor on a 3-phase board


don't know why you would need to break all live conductors here anyhow? i'm sure you can tell me?

 

[malcolmsanford]

Regulation 537.4.1.2 on emergency switching requires that an emergency switch should isolate all lLIVES. There are a couple of exceptions one being if the NEUTRAL is used as a PEN conductor which it should not be in this case. The other being the use of a main linked switch or circuit breaker, which would in the case of a contactor at the origin of the supply could be argued to be a 3 pole, in this case as it will affect equipment through out the building IMO I would use a 4 pole.

Yes there are a lot of things that can be done, but we are talking about a small industrial unit where a certain amount of cost saving would be advisable.

Can I ask why you wouldn't want to isolate the neutral at a 3 phase socket on emergency switching?

 

[davelerave]

-was only a suggestion i threw up for 'consideration'

hey i googled that rule and i think it says you gotta break all lives fot TT
Wiring regulations in brief: a ... - Google Books



just preferable not to switch the neutral through the contactor-things can go pear-shaped downstream

-if the contact gives trouble

 

[malcolmsanford]

That link seems to omit the part of regulation 537.4.1.2 where that section refers you back to reg 537.1.4 which is the 2nd part of my post concerning the origin of supply.

Honestly Dave i'm still wondering what trouble you would have switching a neutral to a 3 phase socket under emergency conditions.

 

[davelerave]

it may not give trouble- i just have an aversion to switching the neutral like that if a contactor is feeding multiple 3p and sp circuits


i don't like it

-no problem on one machine with a balanced load

 

[mgnelec09]

thanks for the advice, the trunking seems like a good idea as by the time i have mounted tray I might as well install trunking and run singles inside.
Cheers

 

[Engineer54]

thanks for the advice, the trunking seems like a good idea as by the time i have mounted tray I might as well install trunking and run singles inside.
Cheers

That would be a much better installation all round, with a far better mechanical protection than SWA. It will also be a more professional looking installation all round too!!

As Malcolm stated nothing wrong in having 3 phase rings, and if now the installation is being considered to be via trunking and conduit, a much easier installation. Like the general purpose ring circuit(s) make these staggered rings which will give you an even spread of load over the circuits.

Not sure if this installation would benefit too much from em-stops, perhaps a single DB em-stop by the main exit door, but apart from that i can't see that this small unit would need anything more. All the stationary/fixed wood working machines would incorporate their own em-stop push.

 

[remer1957]

Only thing I have against three phase rings is that there may be a load of machines on the same ring, with high inrush chracteristics, leading to nuisance tripping, when start-stop at the same times? I would rather wire in XLPE/SWA and tray, I think you may get higher ratings for the same size cables than in trunking and conduit and if done well it looks every as bit as good as trunking and conduit. I wouldn't use plastic conduit in this kind of environment, the amount of workshops I've been in where the conduit has been cracked or smashed and left. How do some of these places get certificated? Also if you use 'C' type glands there is better resistance to ingress of dust/oils etc. You might need more supports/brackets for tray though.

 

[Engineer54]

Only thing I have against three phase rings is that there may be a load of machines on the same ring, with high inrush chracteristics, leading to nuisance tripping, when start-stop at the same times? I would rather wire in XLPE/SWA and tray, I think you may get higher ratings for the same size cables than in trunking and conduit and if done well it looks every as bit as good as trunking and conduit. I wouldn't use plastic conduit in this kind of environment, the amount of workshops I've been in where the conduit has been cracked or smashed and left. How do some of these places get certificated? Also if you use 'C' type glands there is better resistance to ingress of dust/oils etc. You might need more supports/brackets for tray though.

I would have to disagree with you here in part. The integrity and adaptability of using steel trunking and conduit far out ways any advantages of higher current carrying capacities by using SWA cables. Cost and time/labour implications being another...

I originally went along with the SWA cables because i was unsure of the OPs capability of fabricating a traditional trunking/conduit installation, but he now seems quite happy with the idea, so i'm taking it, that he is comfortable working with such materials...

I'm pleased to note, ...that no-one has enquired what a ''staggered ring circuit'' is all about. So at least not all of the old ways have gone west!! ...haha!!!