Board upgrade and new feed tails

[MARK MCCANN]

Morning

Been looking to have my main fusebox swapped (all rcbo type circuits) will need more capacity (especially in the kitchen in the future)
The meter is outside on porch wall and existing fusebox is other side of porch inside, near the ceiling.
Spark is saying that owing to dot and dab plasterboard on porch wall, he has to add in an switch fuse arrangement and a fuse in order to protect the cable as he is unable to get beyond 50mm depth for the cable.
Also because the cable is longer than 3m.

He is also suggesting larger cables (25mm) saying the existing (tails/cables) are 16mm and it would be worth upgrading.
He has said then the electricity board will need to upgrade their fuse to 80 (60) is in now.

The switch that he is talking about putting in also has an RCD as part of it and this projects the tails. The fuse that comes with this switch has an option of 3 sizes and he says he will fit 63amp. Someone else I know said it should be lower than the electricity boards which is 60 now. Although I hope to have it upped to 80. I have read some of the guidelines about upgrading the fuse size from the electricy board and seemingly most can be upgraded (max is 100 apparently) The spark also said there is two more fuse sizes supplied with the proposed new switch box (80 and 100) Is what he is saying ok? And also if the 80 upgrade fuse goes ahead, will the 63 have to be changed to 80? I'm thinking on the extra capacity in the kitchen further down the line.
All pretty much complex stuff and the spark in question appears component and says all will be tested when done and test info on paperwork will be supplied.

Would appreciate any thoughts/info

Tia

Mark

 

[Murdoch]

Hum.

A 60A main fuse for 90% of homes is more than adequate

As for the over 3 m - there are countless installations like this so I wouldn’t be rushing to change the tails

 

[Sharpend]

How much further past the three metres is the new consumer unit going? And what cable type is he proposing?

 

[binky]

normally tails pop up through the cavity, if you have one. Another option would be surface trunking run to avoid RCD protecting tails - not as pretty as proper plaserting tails in, but a lot easier.

60A main fuse - non of his business really. My house has been on 60A since sometime before I bought it, 20 odd years ago.

 

[MARK MCCANN]

Hum.

A 60A main fuse for 90% of homes is more than adequate

As for the over 3 m - there are countless installations like this so I wouldn’t be rushing to change the tails

Cheers

 

[MARK MCCANN]

How much further past the three metres is the new consumer unit going? And what cable type is he proposing?

Only about another metre, possibly 1.5m at most. And in 25mm single core cables (double insulations) 16mm earthing cable

 

[MARK MCCANN]

Hum.

A 60A main fuse for 90% of homes is more than adequate

As for the over 3 m - there are countless installations like this so I wouldn’t be rushing to change the tails

Cheers

 

[MARK MCCANN]

normally tails pop up through the cavity, if you have one. Another option would be surface trunking run to avoid RCD protecting tails - not as pretty as proper plaserting tails in, but a lot easier.

60A main fuse - non of his business really. My house has been on 60A since sometime before I bought it, 20 odd years ago.

Thanks for the reply

 

[Andy™]

Morning


Spark is saying that owing to dot and dab plasterboard on porch wall, he has to add in an switch fuse arrangement and a fuse in order to protect the cable as he is unable to get beyond 50mm depth for the cable.

that would mean the cable needs RCD protection at 30mA. doing so on the tails will make all the RCBO's pointless

find a better spark

 

[Fleeting]

Why would you upgrade the conductors to 25.0 but fit a 63A fuse at the switch-fuse.

 

[MARK MCCANN]

that would mean the cable needs RCD protection at 30mA. doing so on the tails will make all the RCBO's pointless

find a better spark

He's proposing earthed galv cover strip fully fixed and full length of wall and a fused D.P. switch (not RCD) fuse and isolation only

 

[binky]

He's proposing earthed galv cover strip fully fixed and full length of wall and a fused D.P. switch (not RCD) fuse and isolation only

Sounds like a plan . Is this chased into the wall or surface mount?

 

[MARK MCCANN]

Why would you upgrade the conductors to 25.0 but fit a 63A fuse at the switch-fuse.

Spark said it would future proof it. I was thinking 60amp by electric board but 63 in the proposed switch ? Confused?

 

[MARK MCCANN]

Sounds like a plan . Is this chased into the wall or surface mount?

Not sure tbh? Will it need the breeze block chased ? Be some mess I would have thought....it's being plastered over anyway when done

 

[binky]

Not sure tbh? Will it need the breeze block chased ? Be some mess I would have thought....it's being plastered over anyway when done

Then it will be chased into wall to allow plastering over. How deep into the breeze block will depend on the thickness of the current plaster.

 

[MARK MCCANN]

Then it will be chased into wall to allow plastering over. How deep into the breeze block will depend on the thickness of the current plaster.

Thank you for reply. I'll check to see what he is doing......

 

[sirsparkabit]

If I have to fit a switchfuse for a distance of tails longer than 3 metres (usually much further than 3 to a distant C Unit ) I just run SWA

 

[MARK MCCANN]

If I have to fit a switchfuse for a distance of tails longer than 3 metres (usually much further than 3 to a distant C Unit ) I just run SWA

Cheers. Armoured cable he suggested, but on the outside. Guess this could be run on the inside as well.

 

[apprentice87]

Ok, So far as i know, there are no rules, regulations, laws, or anything else that says that if you have tails longer than 3 metres then they have to have an OCPD.

Yes, so far as i can remember the regs do state that a cable over this length has to have an OCPD all of its own, if the cable requires it, [being of a lesser current carrying capacity than the cable that feeds it]

No idea of the cable size that feeds your house or its capacity, but you could argue that the board fuse protects your cable, BUT, the DNO do not like the idea of THEIR fuse being used as protection for the cable, so you can have any tails you like really, how are the DNO going to know?? At the end of the day, a fuse is a fuse and the cable will be protected..

Having said all that, Mr Electrician sounds like he wants to do everything PROPERLY and how it should be. This is no doubt for TWO reasons; 1, he sounds like a good electrician, and; 2, he wants to do it all by the book as it were to prevent future problems..

As for increasing the size of the tails, why not, especially as they will be plastered into the walls...

Finally, how much more would 25mm tails cost?? Errm, not much.. Now [and there is another thread on here that talks about this sort of thing] since the I2R losses are going to be lower using the 25mm cable, there will be a saving to be made over the long term as you will not be wasting money heating the cable up [in theory at least] For tails about 3 meters long and a constant current of 30A you will save about 1 watt so if my maths are right at current [hahaha] prices if you drew 30A 24 hours a day you would save about 0.7 of a penny a day.

Anyway, sounds to me like you have found a very good electrician, so my advice is to let him get on with it..

john..

 

[Andy™]

Ok, So far as i know, there are no rules, regulations, laws, or anything else that says that if you have tails longer than 3 metres then they have to have an OCPD.

433.3.1(iii) & 434.3(iii)

basically if DNO don't agree (i.e over 3m, or whatever they say) then 7671 requires overload / fault protection