Thoughts please

[durhamspark]

Coincidently I'm just looking at something along these lines at this very moment. Scenario is I need a 298 amp flc 3 phase supply to run a compressor but the panel board is obselete and I'm struggling to get hold of a 320 amp mccb which can be adjusted down to 300. The one I can get is 400 amp, adjustable to 320, but my cable calculations came out with 95mm with a max load of 304 A.

I have 2 possible options, 1 is to upgrade the cable to 120mm which I don't want to do if possible due to cost and slightly harder to terminate into connections etc.

Other option is rather than an isolator at the compressor end, use a fuse switch and 300A fuses to limit overload current.

What do you reckon? It'll undoubtably come down to cost in the end

P.s option 3 would be a new panel board but the implications of shutting the plant down are huge

 

[NickD]

Short run of 120mm to a new small sub board where you fuse down to 300A and then run from that to the compressor in 95mm? I don't know industrial electrics so I'm just going from first principles. And hopefully learning as I go.

 

[D Skelton]

If the full load current is 298A and your cable's ccc is 304A then the only option IMHO is a fused switch (as opposed to a switch fuse) at the load end providing your supply cable is protected against fault current in accordance with section 434.

 

[NickD]

Why don't you think my sub board is an option?

 

[D Skelton]

It's not that it isn't an option because it is, but it would be an unneccessary and costly option.

 

[durhamspark]

If the full load current is 298A and your cable's ccc is 304A then the only option IMHO is a fused switch (as opposed to a switch fuse) at the load end providing your supply cable is protected against fault current in accordance with section 434.

That's what I'm leaning towards, I thought I said fused switch rather than switch fuse.

No space to fit a sub board and it would work out costly, MEM are already taking the p*** with the MCCB so I'll be looking for a different brand fused switch to the glasgow I was going to get.

I'll be having a look at the fault current calculation tonight, and looking on ebay for a MCCB!

Thanks for the advice, any opinions on a fused switch with plenty of room to terminate cables? looking like I'll need a couple of spreader boxes.

 

[D Skelton]

any opinions on a fused switch with plenty of room to terminate cables?

I'd be looking at a Glasgow, but... lol

Try Hager or ABB

 

[durhamspark]

I'd be looking at a Glasgow, but... lol

Try Hager or AAB

Would normally get a glasgow myself but feel like they are trying to hold me to ransom over the breaker so that's got my back up a bit!

 

[durhamspark]

Grrr!, can't get 300amp fuses only 315's so back to square 1.

Maybe some kind of MCCB in an enclosure at load end?

 

[D Skelton]

Unfortunately when you're talking upwards of 200A you know you're gonna get stung with three figures! This is the cheapest I found one for:

Eaton MEM 303GNC Glasgow Grey Three Phase TPN Fuse Switch Disconnector 315A - TOB International Ltd

Just swap out the fuses for 300A ones

 

[durhamspark]

It's the fuses I'm struggling with. Looks like they jump from 250 to 315.

I might have to postpone the job until I can get a 320 a adjustable mccb .

Failing that bite the bullet and go with 120mm cable

I fully expected to pay that for the fused switch but they are asking 1300 + vat for an mccb !

 

[D Skelton]

It's the fuses I'm struggling with. Looks like they jump from 250 to 315

Buy Bolted Tag Fuses BS88 GSGB ultra fast acting fuse,300A GE Power Controls GSGB300 online from RS for next day delivery.

And Robert's your father's brother!

 

[mandrake]

Each 20A load would need a 20A fuse to protect the 2.5, surely without this then is one of the loads increased through whatever reason, the 2.5 would melt well before the 100A tripped.
I'm with shanky887614 on this one.

 

[durhamspark]

Buy Bolted Tag Fuses BS88 GSGB ultra fast acting fuse,300A GE Power Controls GSGB300 online from RS for next day delivery.

And Robert's your father's brother!

Champion , there's the job sorted. As luck would have it I've managed to locate a 320a Mccb so no need for them now but I have a back up plan in case it goes before I get the order .

Glad I had these problems in a way cos it does no harm to get the grey matter working and do a few calculations to solve a problem . Thanks for the help, much appreciated

 

[Davehaywire]

2.5mm 100a mcb over-rated