Two recent threads about moving a CU mentioned that an additional 100 Amp DP isolator was fitted after the meter. When is this necessary?
As my installation doesn't have one I will need to break the seal and pull the cutout when I eventually swap my CU for a 17th edition one.
Meter is in cupboard outside, and about two meters of tails though the porch wall to the CU. Supply is TN-S (I think).
It's not - it's a convenience to save pulling the cutout fuse.
You could install your own at that time - it's nothing more than a 100A DP main switch (from a CU) fitted in a nice Wylex slimline housing with 4 entry holes optimised for meter tails.
Depends on the DNO, but if the tails are more than 3m some insist on a switch-fuse to provide overcurrent protection to the tails.
Isoaltor only:
"It's safer because the supply tails are fixed and finalised in a sealed unit - instead of being left hanging loose ready to connect to the meter."
I was puzzled by that. From what they did in my place I inferred it mean that the consumption-side installer installs consumption-side tails into the isolator, and the the supplier comes along and installs the supply-side tails into the isolator; instead of installing the CU and leaving a pair of tails dangling for the supplier to wire into their meter.
JGH
ITYM 'left hanging loose ready to connect to the CU"
If the supply-side tails are installed first they can be installed into the supply side of the isolator and the isolator locked off. Then there are no live parts. The customer-side tails go into the dead customer-side of the isolator and the isolator is only unlocked when everything's nice and safe.
No pulling the Big Fuse, no risk of arcing, etc.
In some fit-outs the supply and meter will go in before the CU and internal wiring so there are no customer tails to connect at that time.
Owain
JOOI what spec does the cut out isolator switch have to be?.
Would a 100 amp one in a wall mounted 2 Units wide DIN rail enclosure be sufficient?...
Like these?..
An isolator is just a DP main switch in a suitable housing - yes the above would work.
The Wylex REC2S is a bog standard main switch in a highly optimised housing.
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