What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut out

flyingsparc · Apr 27, 2012

Hello,

I wanted to know what others would do with this situation.

Currently the house that I am going to rewire and replace CCU on has (starting at distributers cut out installed externally in box) from 60A fuse/service head are 16mm tails to meter, from meter 16mm tails to 100A DP isolating switch, from DP 10mm MICC to existing CCU approx 5 meters away.

Am going to replace the 10mm MICC with either either 16mm or 25mm SWA (max. current carrying capacity of 10mm PVC sleaved MICC clipped dircet =77A)

As the tails from DP to CCU are over 3m in length, I have to install a SP&N switchfuse within the first 3 meters. I will prob. remove DP isolator in external box and put switchfuse in there if there is room and ownership of box cannot be 100% established.

So finally to my question - if the distributers cut out is 60A what rated fuse would you put in the switchfuse?

All suggestions welcome.

Thanks.

Guest55 · Apr 27, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

Some may say 40A to achieve discrimination.
I'd just use 60A anyway to give the consumer the most current available.

Guitarist · Apr 27, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

As biff says, you really need to give the customer the 60A available.

Knobhead · Apr 27, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

Why are you replacing MICC with cheap crap?

50A fuses are available

londonlec · Apr 27, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

Just replace DP switch with a 60a switch fuse. Leave the existing MICC as it is.

Des 56 · Apr 28, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

There is no need or requirement to provide discrimination with the suppliers fuse
You size your fuse to your own installation

If you tried to discriminate,you would probably need a fuse at least half the rating of the suppliers and even then,discrimination would be hit and miss which would go first
If either goes the effect is still going to be the same ie loss of supply

Edward Amsden · Apr 28, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

How many boards do you see that have the potential of drawing 100A which have 16mm tails to a 60A distributors fuse. At the end of the day it is safe as the fuse is rated to the tails

RISElectrical · Apr 28, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

60A fuse and leave the micc in place, it will out last whatever you install haha

flyingsparc · Apr 29, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

Many thanks for all of your replies. So I'm going to use a 60A in the switchfuse, and understand the view to keep the 10mm MICC, calcs ok etc. Problem is that the OSG says (2.2.3 page 17) min cable size should be 25mm². Other than future distributor upgrades I cant see why this is stated? This doubt could be my misinterpretation of the word ‘should’ (the minimum cable size should be 25mm²)….. it doesn’t say ‘must’!

Thanks again.

Guest55 · Apr 30, 2012

Re: What fuse rating in SP&N switchfuse would you use on domestic supply with 60A cut

The tails only need to be 25mm from the meter to the first piece of the consumers switchgear , after being fused down the sub-mains can be a smaller sized cable to the consumer unit.