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Topic Title: Understanding Split single phase installations.
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Created On: 10 April 2017 11:41 AM
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 21 April 2017 12:06 PM
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AJJewsbury

Posts: 15855
Joined: 13 August 2003

I don't see why you can't use a standard 415V 3-phase board. Standard 3-phase equipment is rated for 240V to earth, 415V between phases. 415V between phases means in reality 415V between L1-L2, and 415V between L2-L3. So insulation withstand between L1-L3 will be 830V in reality for conventional flat formation busbars and switches (and it's a long time since I've seen triangular formation busbars at LV). If you use L1 and L3 (not your suggestion of L1 and L2) then you're fine.

On a type-B bus-bar assembly, with the main bars running vertically, don't the tap-off connections run horizontally in front or behind the main bars? - so may only have a single layer of insulation (400/415V worth) between them and the one or two main bus-bars they cross?
- Andy.
 21 April 2017 12:49 PM
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di515223

Posts: 337
Joined: 08 July 2010

At 480V split phase with Neutral as described, it seems to me that the economies of this rapidly disappear.
Surely not only the initial distribution board, but all other switchgear handling the 480V supply will need to be suitably rated, including isolators, fusegear etc. You say you are going to distribute this about the site, so you will need more than one distribution board rated at theis voltage - you need the main one, plus one for avery building using the 480V supply ( so at least one more). What is the PSC the initial board will have to cope with, and what about the downstream sub-mains? a 500A Supply is going to need a fairly large board anyway, so I am wondering if the overall cost has been fully calculated.
What cables are you planning to use for distribution?

Dave
 21 April 2017 10:03 PM
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mapj1

Posts: 9383
Joined: 22 July 2004

I don't see why you can't use a standard 415V 3-phase board. Standard 3-phase equipment is rated for 240V to earth, 415V between phases. 415V between phases means in reality 415V between L1-L2, and 415V between L2-L3. So insulation withstand between L1-L3 will be 830V in reality for conventional flat formation busbars and switches (and it's a long time since I've seen triangular formation busbars at LV). If you use L1 and L3 (not your suggestion of L1 and L2) then you're fine.

On a type-B bus-bar assembly, with the main bars running vertically, don't the tap-off connections run horizontally in front or behind the main bars? - so may only have a single layer of insulation (400/415V worth) between them and the one or two main bus-bars they cross?
- Andy. I don't see why you can't use a standard 415V 3-phase board. Standard 3-phase equipment is rated for 240V to earth, 415V between phases. 415V between phases means in reality 415V between L1-L2, and 415V between L2-L3. So insulation withstand between L1-L3 will be 830V in reality for conventional flat formation busbars and switches (and it's a long time since I've seen triangular formation busbars at LV). If you use L1 and L3 (not your suggestion of L1 and L2) then you're fine.

On a type-B bus-bar assembly, with the main bars running vertically, don't the tap-off connections run horizontally in front or behind the main bars? - so may only have a single layer of insulation (400/415V worth) between them and the one or two main bus-bars they cross?
- Andy.


Indeed, and we all know electrically it will be just fine, because it is all tested at 4kV anyway.
The problem is purely one of paperwork and liability.

Must admit if it was being built up to order, at least for the normal part I'd have expected to see two single phase style bus bar combs, one each side so we have all phase 1 on the left, and all phase 2 on the right, and probably link cables to the main breaker. Equally I haven't seen one for ages

-------------------------
regards Mike
IET » Wiring and the regulations » Understanding Split single phase installations.

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