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?

 

[timo]

Meter tails max 3m away with no Switch fuse. So your 16m would need a switch fuse.
So your setup would be Meter - Isolator - Switch Fuse - Tails - C.U

Not sure how you would need to protect tho. Also would you need to RCD protect after the Isolator to the C.U ?

 

[Spudnik]

1. Not necessarily.

2. Yes.

 

[AEC]

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?

In answer to your questions;

1. If you are installing Meter Tails then the will be BS6004, Double Insulated just like a Twin and Earth. Both Live, Neutral and Earth should be kept together along the route.

2.Using the above method will require a RCD and Over Current Protection after the DNO Isolator.

If you were to install a SWA then no RCD would be required, just Over Current Protection.

Would be interested to know how much DNO charges for fitting the switch.

 

[lamb]

DNO doesn't fit the switch in my area, its the Meter Operator working on behalf of the Energy Supplier.
Cost usually 45-65 pounds. Which is a very fair price.

In this case a switch fuse will be required, wylex make them. Use metal clad for SWA or insulated for tails.

Disagree about the RCD protection, unless the cables are concealed in a wall (assuming TN system).

 

[Sintra]

Also disagree with the RCD protection if the cables are surface clipped below the floor and run surface into new cu.

 

[sidekick]

Thanks all.
Thought switch fuse would be needed so just making sure.
Had planned to use mem/kmf switched fuse. Anyone got any advice on better or easier product.
For the sake of making sure, RCD switched fuse would be ok even though tails will be clipped under floor. Anyone able to suggest best option for that.

The meter, Isolator switch and switched fuse will all need to be concealed in a cupboard in what will become a bedroom, least obtrusive options preferred.

Will avoid working with 25mm SWA if possible as long as safety not compromised.

Normal cost for Isolation switch usually 45 to 75 pounds. I would always recommend that route as it keeps everything safe and legal and avoids messing with any pulling of fuses etc. Small price to pay.
I may also add that on many occasions the fuse has been fitted free (not sure if intentional or if they just forget to invoice)

 

[martysparky]

I think its a far price for isolation switch and like that method.

Pricing the job is another story though.

 

[lj.l]

What about discrimination,if you are usuing a rcd to protect the mains do you use a time delayed one ?otherwise it might trip before any rcbo/rcd fitted in the consumer unit does.

 

[baldsparkies]

What about discrimination,if you are usuing a rcd to protect the mains do you use a time delayed one ?otherwise it might trip before any rcbo/rcd fitted in the consumer unit does.

You have just given a good reason for sticking with swa surface clipped from the switch fuse to the consumer unit. The switchfuse will give overcurrent protection for your swa. And no rcd discrimination problems between in line rcd's because your rcd protection starts from the consumer unit and not your sub main feed.

 

[sidekick]

You have just given a good reason for sticking with swa surface clipped from the switch fuse to the consumer unit. The switchfuse will give overcurrent protection for your swa. And no rcd discrimination problems between in line rcd's because your rcd protection starts from the consumer unit and not your sub main feed.

Looks like its all down to -
a) work with 25mm SWA (3 core I assume for line, neutral and earth)
or
b) 25mm tails from time delay RCD switch fuse.
????

 

[baldsparkies]

Looks like its all down to -
a) work with 25mm SWA (3 core I assume for line, neutral and earth)
or
b) 25mm tails from time delay RCD switch fuse.
????

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

 

[trix]

Why not use 16mm 2 coew swa ?

 

[sidekick]

Why not use 16mm 2 coew swa ?

Thought tails needed to be 25mm ??
I assume you also then mean run 16mm earh seperately.

 

[Guest123]

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.

 

[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.