3 phase isolator

[sparkie-leeds]

Hi All,

The electric board are installing a new 3 phase supply in to the building, they are asking for a 3 phase isolator which is not a problem. From the 3 phase isolator i am running a 4 core 25mm armoured cable with seperate 16mm cpc to a mains board. What i want to know does the 3 phase isolator have to be FUSED, the incoming fuses are 100amp supplied by the elctric board in the main head.

The isolator will be rated at 100 amp aswell.

thanks.

 

[i=p/u]

If under 3 m no I think, but wait.....

 

[plugsandsparks]

depends, but mmmmm what size fuse to use ?

 

[ipf]

Why, with the 100amp incomming ?

 

[plugsandsparks]

think you have mentioned already why a fuse may be approrpiate, but would you fuse it down just to get a discrimination or not bother, i probably wouldn't.

 

[sparkie-leeds]

think you have mentioned already why a fuse may be approrpiate, but would you fuse it down just to get a discrimination or not bother, i probably wouldn't.

I will not be down fusing it

 

[sparkie-leeds]

the 25mm is adequate for the load so would i need to fuse the isolator

 

[plugsandsparks]

Sometimes simpler is better, i cannot see the point of two 100A fuses in series, probably cause more confusion during faulting.
Dont know the swa run but you can always give it extra protection,

 

[sparkie-leeds]

i don't neither but wanted to check with you guys, all they want is an isolator switch, its fused at the main head, its surley for isolation purposes only.

 

[ipf]

If you want to protect the DNO, fuse down to 80amp. Reason.... unlikely damage to swa? Depends on the cable run, I'd say.

 

[sparkie-leeds]

the cable run is approx 20mtrs pulling approx. 60 - 70amps per phase

 

[bryanh]

UK Power in our area only ever ask for a Isolator, if you fit smaller fuses then you are limiting your suppy load so I would say no need to fit fuses, if you still not sure ask your area supplier they will advice what you need m8

 

[sparkie-leeds]

UK Power in our area only ever ask for a Isolator, if you fit smaller fuses then you are limiting your suppy load so I would say no need to fit fuses, if you still not sure ask your area supplier they will advice what you need m8

I don't feel there is a need to fuse the isolator as its fused at the head, approx. 2 mtrs away from the isolator, just wanted to check.

 

[electric will]

Surely this needs to be fused as the swa from the isolator to db is over 3m long?

 

[sparkie-leeds]

Surely this needs to be fused as the swa from the isolator to db is over 3m long?

why would you put 2 lots of 100amp fuses in serious