Consumer Unit further than 3 metres from the metering position

[batty]

I think KME has already clarified, but NO RCD required for TNS or TNCS.It may be required for TT to provide Shock protection as earth loop impedence will likely be more then max Zs for the Distribution cct.

Why Switch FUSE?

The DNO will only allow THEIR Service fuse to be used to protect YOUR Meter tails up to 3 Meters in length. More then that then YOU have to provide Fault and overload protection.

If cables are concealed they are going to need 30mA Rcd protection unless they are protected by earthed metal or earthed swa so that will not comply with 17th. You also will need an 80 amp switchfuse if its a 100 amp supply so if there is a problem your fuse will go before supply fuse.

 

[Lee321]

yep last 2 replys just wanted the right info in the thread

 

[maccarooni]

If cables are concealed they are going to need 30mA Rcd protection unless they are protected by earthed metal or earthed swa so that will not comply with 17th. You also will need an 80 amp switchfuse if its a 100 amp supply so if there is a problem your fuse will go before supply fuse.

What if its an 80amp supply, 80A switch fuse, or dp isolator?

 

[Lee321]

can't see how the 80 or 100a makes a difference if the tail size is 100a capable

 

[WhitleyElectrical08]

it`s a tn-c-s system and i think the answer is running a new 25mm swa to the consumer unit from 100A sw fuse in the meter box even tho the builder wants it done as cheap as poss!! (which they always do) Thanks for your input guy`s. In answer to jud`s question its because the architect is a pain in the arse!

 

[Nicky Tesla]

1. There is double page spread in this months professional electrician at the wholesalers about this subject.

2. Can we use split concentric cable.

 

[300TDI]

Use an 800kmf for 80a

http://cgi.ebay.co.uk/Switch-Fuse-800KMF-80A-/330434568894?cmd=ViewItem&pt=UK_BOI_Materials_Supplies_Electrical_ET&hash=item4cef6f62be

Not mine, but an example for your info

 

[Andy™]

2. Can we use split concentric cable.

yes. but for RCD's is same conditions as T&E

 

[batty]

What if its an 80amp supply, 80A switch fuse, or dp isolator?

If you have 80amp main fuse technically you should have 60 amp in your isolator.

 

[Lee321]

If you have 80amp main fuse technically you should have 60 amp in your isolator.

:Applaud

 

[wozz]

do you really have to try to achieve discrimination in this situation?

 

[Sidewinder]

Would a 60A gG & an 80A gG actually achieve discrimination?

At these close ratings manuf' data and other suble issues may come into play.

The pre-arcing time would need to be considered as would the neregy let through.

Also different manufacturers may have different characteristics in their fuses.

Remember BS requirements are worst case, so a "worst" case downstream fuse may not discriminate against a "best" case upstream fuse.

 

[Lee321]

do you really have to try to achieve discrimination in this situation?

probably not for true discrimination but the regs say you should reduce inconvenience so by not having a fuse in your isolator that will blow before the cutout fuse could be deemed as inconvenient as you'd have to wait for dno to replace.

 

[wozz]

i can see what you are saying but the same could be said for every other installation that doesnt need a switch fuse. If i dont install a switch fuse am i causing inconvenience?

what if the dno stick a 60A fuse in there? (if they still do)

 

[Andy™]

What if its an 80amp supply, 80A switch fuse, or dp isolator?

not that im suggesting anything... but changing the service fuse to 100A would fix the problem....

 

[ianmacd]

Incidentally, the 3m rule is from the cut out and needs to include the length to the meter.

 

[Voltimax]

Incidentally, the 3m rule is from the cut out and needs to include the length to the meter.

Just to add my 2 penneth, it isn't the 3mtr rule, some DNO's may state 2mtr. Read the latest professional electrician magazine, its been covered by the NICEIC.

 

[ianmacd]

Just to add my 2 penneth, it isn't the 3mtr rule, some DNO's may state 2mtr. Read the latest professional electrician magazine, its been covered by the NICEIC.

Well if the NIC said it, it muct be true .

 

[Voltimax]

Well if the NIC said it, it muct be true .

ROTFWL

Actually I was once told by the DNO here that it should be no more than 2mtrs. It's always been either 2mtr or 3mtrs, never any more and never any less.

 

[M107]

I've got a nice one I've just quoted on....TP&N service head is 28.4 meters away from the proposed DB location....

KEEEEEERRRRRRRCHING on that swa