Switched fuse on meter tails ?

[sidekick]

I have a consumer unit change which also means relocating the unit approx 16m away from original position where meter is.
I have (as i always do) arranged for YEDL to come and fit an isolation switch first.
Once this is done the new meter tails will go from the switch under the floor for approx 15m and back up to new position.

My questions are -

1. Do i need to use any form of protection for the meter tails uder the floor or just clip to the underside of the joists?

2. Do I still need to fit a switched fuse after the isolation switch?

 

[sidekick]

As you are installing a switchfuse between the cut-out and the DB, your outgoing tails can be 6mm if you like, providing you use the correct size fuse for 6mm.

Obviously we dont do that and 16mm or 25mm is the norm. If you're using a 60A fuse then 16mm tails are fine, 80A or 100A then 25mm.

Thanks Lenny,
To decide 60A or 80A switched fuse -
maximum demand on DB to be calculated which I think will be in excess of 60A and therefore would 60A fuse be enough ?
and do I need discrimination with main cut out fuse which may 100A but more and more are being downrated to 80A ? (I will have that confirmed when DNO fits isolator switch)

 

[thewyresparky]

I would like to say thanks for this post as I am doing an allmost identical job and you have answered everything for me too. The only difference is my run is 6 mtrs and will be run in trunking, So no RCD required between fused switch and CU, if i understand correctly. Thanks.

 

[GLENNSPARK]

I would like to say thanks for this post as I am doing an allmost identical job and you have answered everything for me too. The only difference is my run is 6 mtrs and will be run in trunking, So no RCD required between fused switch and CU, if i understand correctly. Thanks.

get yourself a bit of 3 core 25mm CSA armoured.....

 

[thewyresparky]

Will do, Thanks for the advice, much appreciated.

 

[Outspoken]

Guys, FFS, has anyone considered VOLT DROP here??

Normal meter tails are 25mm² DI, contrary to the plonker who suggested running it in BS6004 DI (Ye Har), It MUST be treated as a sub-main at that distance and as such should be SWA (unless you intend Pyro..hahahaha). Sub-mains need to be Isolated at the supply end and the cable is yours and not the DNO so you must also install fault protection (overload-does not require RCD). But you cannot just say "Oh I know, I'll do it in 25mil armoured and it'll be fine".

You must consider the load this will be put to and do the calculations to ensure that;

• The Cable is sized correctly
• The Volt Drop is within limits
• The Disconnection time is within limits
• It meets the requirements for Mechanical Protection (Clearly SWA does)

Now it is likely that 25mm² SWA will meet all the above and be fine, but you cannot just assume it will.

 

[GLENNSPARK]

Guys, FFS, has anyone considered VOLT DROP here??

Normal meter tails are 25mm² DI, contrary to the plonker who suggested running it in BS6004 DI (Ye Har), It MUST be treated as a sub-main at that distance and as such should be SWA (unless you intend Pyro..hahahaha). Sub-mains need to be Isolated at the supply end and the cable is yours and not the DNO so you must also install fault protection (overload-does not require RCD). But you cannot just say "Oh I know, I'll do it in 25mil armoured and it'll be fine".

You must consider the load this will be put to and do the calculations to ensure that;

• The Cable is sized correctly
• The Volt Drop is within limits
• The Disconnection time is within limits
• It meets the requirements for Mechanical Protection (Clearly SWA does)

Now it is likely that 25mm² SWA will meet all the above and be fine, but you cannot just assume it will.

eh?...ffs...what kind of a statement is this?

 

[Outspoken]

eh?...ffs...what kind of a statement is this?

It means at the supply end you need to ensure their is overload protection but there is no requirement for RCD. This SHOULD be installed in the consumer unit unless fitting RCBO's.

 

[shocking_eg]

SWA for submains any day !!!

sod having meter tails left under the floors ready to get damaged ! lol

 

[newbiespark]

For what its worth, I would go with option, a) all day long

Sorry to dig up a really old thread, but I've got exactly the same job to do and I just wanted to double check.

Would there be a problem to run 2-core 25mm SWA and then a separate 16mm single earth? Just trying to make life easier manipulating cables around corners and through joists etc...

Any thoughts?

 

[telectrix]

Sorry to dig up a really old thread, but I've got exactly the same job to do and I just wanted to double check.

Would there be a problem to run 2-core 25mm SWA and then a separate 16mm single earth? Just trying to make life easier manipulating cables around corners and through joists etc...

Any thoughts?

as long as they follow same route and armour is earthed.

 

[newbiespark]

as long as they follow same route and armour is earthed.

Perfect - thanks for confirming.

 

[pc1966]

I would just add that you should make sure the armour is earthed at both ends (i.e. armour wire is in parallel with the 16mm earth) to keep the cable Zs down to a value that allows the sub-main to meet 5s disconnection on your chosen fuse on any internal fault.

 

[newbiespark]

I would just add that you should make sure the armour is earthed at both ends (i.e. armour wire is in parallel with the 16mm earth) to keep the cable Zs down to a value that allows the sub-main to meet 5s disconnection on your chosen fuse on any internal fault.

Will do - thanks!