3 Phase Distribution Board Dilema

SparkingMad1997 · Nov 29, 2023

Hello All

So I'm not long out of my college days and unfortunately I didn't have a lot of exposure to three phase and commercial wiring systems. I have a three phase switch fuse Isolator rated at 200Amp supplied by the landlord. I need to split this across two Proteus distribution boards, the main switches and Busbars are rated for 100 amps 3 phase. I need the full 200amps so I can't just swap the fuses out in the Isolator. So my question is... between the boards and Isolator how would you go about fusing down? A 6 way ryefield, 100 per phase?

Thanks

westward10 · Nov 29, 2023

Three phase or single phase Proteus boards?

SparkingMad1997 · Nov 29, 2023

westward10 said:
Three phase or single phase Proteus boards?

Three phase

westward10 · Nov 29, 2023

SparkingMad1997 said:
Three phase

I reread your first post and realised. Are you sure they aren't 125A?
If you need the full 200A and have space just install additional switch fuses.

pc1966 · Nov 29, 2023

Can you fit a 100A MCCB incomer to those Proteus boards?

If so just make sure all the cable up to each board's incomer is rated to clear the 200A fuses.

Flanders · Nov 29, 2023

I see 3 options.
4 way to mccb panel
Ryfield unit
or bus bar chambers with 2x 100 amp switch fuses or with some DBs you can fit a mccb to use as the main switch. Schieder is one example I know of.

SparkingMad1997 · Nov 29, 2023

Wow a few options coming at me here.

Sooo MCCB option, seems like a viable idea but then I'd need to bolt 2 sets of 95mm tails to the switch fuse unless a busbar chamber is used?? In which case we may as well just fit one 95mm tail and use fuses in the chamber?

Please forgive my lack of knowledge on commercial, I'll try to keep up!

pc1966 · Nov 29, 2023

First you need to see if you can get MCCB incomers - a quick look at the CEF site for Proteus was not too hopeful (only seem to have isolator switches), but worth asking them for that.

Next big point is how far is each TPN board from your 200A switched-fuse? If it is a short distance then it is reasonable to use incomers (if available!) and 200A cable, but if a significant distance to one or the other then fusing down at origin is a better plan.

As @Flanders suggested you can do the split in several ways: MCCB boards are good for complicated set-ups and if unskilled people might have to reset a breaker, but fuses in the form of a pair of switched-fuses or a small Ryfield board are often cheaper and have a better trade off in terms of operating current versus end of cable Zs to meet 5s disconnection (assuming TN here).

SparkingMad1997 · Nov 29, 2023

pc1966 said:
First you need to see if you can get MCCB incomers - a quick look at the CEF site for Proteus was not too hopeful (only seem to have isolator switches), but worth asking them for that.

Next big point is how far is each TPN board from your 200A switched-fuse? If it is a short distance then it is reasonable to use incomers (if available!) and 200A cable, but if a significant distance to one or the other then fusing down at origin is a better plan.

As @Flanders suggested you can do the split in several ways: MCCB boards are good for complicated set-ups and if unskilled people might have to reset a breaker, but fuses in the form of a pair of switched-fuses or a small Ryfield board are often cheaper and have a better trade off in terms of operating current versus end of cable Zs to meet 5s disconnection (assuming TN here).

So my set up is all confined to a small intake room where you couldn't even swing a piece of conduit at the apprentice. I have a roughly 800mm length of 4inch trunking with the Isolator on top, the main dB to the right and a 500mm space between the board and Isolator on top of the trunking for a Ryefield. This seemed like the easiest option and one which I've has experience with! Cost the factor which has lead me here.

westward10 · Nov 29, 2023

I doubt Proteus do 947-2 incomers.

westward10 · Nov 29, 2023

Why the two boards are they metered separately?

davesparks · Nov 29, 2023

SparkingMad1997 said:
Sooo MCCB option, seems like a viable idea but then I'd need to bolt 2 sets of 95mm tails to the switch fuse unless a busbar chamber is used??

No, you'd only need one set of conductors from the switchfuse to the MCCB distribution board, then suitably sized outgoing conductors from each MCCB.

I had to do pretty much the same thing on this job, take an existing 200A feed and split it down to 2x 100A feeds. Previously the fuses in the fuse-switch had been changed to 100A to feed the one outgoing distribution circuit. I needed to add a second distribution circuit so swapped the fuses back to 200A and fitted the MCCB board.
(Yes I fixed the gap in the trunking lid)

The board is an MG25C2 Scheider Merlin Gerin MG25C2 Powerpact 4 - 13 SP Ways, 250A Panelboard - https://electricalwholesalers4u.com/products/scheider-merlin-gerin-mg25c2-powerpact-4-13-sp-ways-250a-panelboard?variant=44704876888310&utm_source=google&utm_medium=organic&utm_campaign=Shopify%20Custom%20GMC%20Feed&utm_content=Scheider%20Merlin%20Gerin%20MG25C2%20Powerpact%204%20-%2013%20SP%20Ways%2C%20250A%20%20Panelboard&gad_source=1&gclid=Cj0KCQiA35urBhDCARIsAOU7QwkSOymDJNpGhIUA29hoH4fm2Mx-5DhK5dkP9ueAsGsdRUrUqr7CY-MaAksFEALw_wcB

[ElectriciansForums.net] 3 Phase Distribution Board Dilema

davesparks · Nov 29, 2023

SparkingMad1997 said:
I have a roughly 800mm length of 4inch trunking with the Isolator on top, the main dB to the right and a 500mm space between the board and Isolator on top of the trunking for a Ryefield. This seemed like the easiest option and one which I've has experience with! Cost the factor which has lead me here.

The easiest option isn't necessarily the best option and the cheapest option is rarely best.

Fuses vs MCCBs both have their pros and cons.
MCCBs offer convenience of being easily resettable.
With the Ryefield option the whole installation would need to be isolated to replace 1 fuse (removing/reinstating fuses into a live board is hard to justify in a risk assessment without a good reason and expensive arc-flash PPE)

pc1966 · Nov 30, 2023

davesparks said:
The easiest option isn't necessarily the best option and the cheapest option is rarely best.

Fuses vs MCCBs both have their pros and cons.
MCCBs offer convenience of being easily resettable.

Very true!

davesparks said:
With the Ryefield option the whole installation would need to be isolated to replace 1 fuse (removing/reinstating fuses into a live board is hard to justify in a risk assessment without a good reason and expensive arc-flash PPE)

As there is a 200A fused-switch feeding it then easy to do, and if 100A fuses feeding the TPN boards they should be no more likely to be blown than typical house DNO fuses, and will have total selectivity with the 200A ones.

Assuming sensible distribution of loads, overall demand, etc.!

Rockingit · Nov 30, 2023

SparkingMad1997 said:
Wow a few options coming at me here.

Sooo MCCB option, seems like a viable idea but then I'd need to bolt 2 sets of 95mm tails to the switch fuse unless a busbar chamber is used?? In which case we may as well just fit one 95mm tail and use fuses in the chamber?

Please forgive my lack of knowledge on commercial, I'll try to keep up!

Don't forget that 434.2 allows for positioning of the over-current protection to be downstream of the device where downstream protection exists (so your MCCB incomer). As such, you may only need 35mm tails which the vast majority of switchgear would accept being double-lugged (normally one behind and one in front of the bus bolt).

3 Phase Distribution Board Dilema

SparkingMad1997

westward10

SparkingMad1997

westward10

pc1966

Flanders

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SparkingMad1997

pc1966

SparkingMad1997

westward10

westward10

davesparks

davesparks

pc1966

Rockingit

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