Main Fuse Capacity

[Tonyx]

Hi,

Could someone please advise me how to work out the max load permissable for a 60A main fuse. I want to fit a 8.5kw shower which requires a 40A fuse and replace the CU. The existing CU (Memera 3) has a 30A cooker fuse (spare) a 15A water heater fuse (spare) a 30A ring final circuit and a 5A lighting circuit.

I have heard somewhere that if the board does not have 100A capability, then a circuit above 32A must not be installed onto it. Is that correct?

I am doing this job as one of my niceic assessments so I need to be spot on.

Many thanks,

Tonyx

 

[securespark]

I would advise the DNO of your intention to add a high-powered electric shower to the already stretched installation on a 60A fuse & see if you can wangle an upgrade.

 

[Tonyx]

Thanks I'll give that a try but, is it true that 'if the board does not have 100A capability, then a circuit above 32A must not be installed onto it'?
If so, where does it state that for my reference? and, can I still do the job if they won't agree to an upgrade?

As mentioned the existing CU (Memera 3) has a 30A cooker fuse (now spare) a 15A water heater fuse (now spare) a 30A ring final circuit and a 5A lighting circuit and a label stating max load of 80A.

Thanks,

Tonyx

 

[securespark]

It is best to seek guidance from MEM: ring 0161 652 1111. Sorry, the number's changed to 655 8900. Ask them if it is advisable to add such a load to their board.

 

[sparkybird]

In theory, you should work out the maximum demand (allowing for diversity) and see if your main fuse is sufficient.

In reality though I doubt if DNO will be interested. In my early days I wanted to install 50A shower for client, main head 60A and house had usual circuits. DNO duly came out and told me to 'stop faffing around and just get on with it'. Looked a right t*t in front of the customer!

You have to be drawing 60A for a long time for the fuse to blow, so unless you take very long and hot showers.....


SB

 

[Tonyx]

Thank you for taking the trouble to reply, much appreciated.

The maximum demand on the existing CU was 80A (2x30A, 1x15A, 1x5A) and the CU had a label on it saying do not exceed 80A. I'm replacing the CU and want to install a 40A shower. I have got rid of 1x30A and 1x15A (not required) so the maximum demand on the new CU will be 1x40A, 1x 32A, 1x6A (bathroom lights) on an RCD and 1x6A (other lights) on the main switch. Total 84A. Not sure how to calculate diversity

I have asked EDF for a main fuse upgrade to 100A, which they have agreed to do, subject to some paperwork and a 8 week lead time. So, I can do the CU change for the niceic assessment and install the shower at a later date.

Cheers,

Tonyx

 

[sparkybird]

Tonyx

No prob. I suggest you read up on diversity as you might be grilled on it for the NIC assessment (I know I was!). Have you got a regs book or on site guide? Have a look in there....
SB

 

[Tonyx]

Will do, many thanks!

 

[Space cat]

I have asked EDF for a main fuse upgrade to 100A, which they have agreed to do

and

the CU had a label on it saying do not exceed 80A

 

[ban-all-sheds]

 

[Space cat]

Nice one BAS! It took a while but I got there in the end.



PS: Please excuse the multiple smileys.

 

[Tonyx]

Not sure why I'm being quoted out of context but if there's a joke out there lets all share it..............

The old CU had a label saying 'do not exceed 80A' so I've asked for a main fuse upgrade to enable me to install an 8.5kw shower and.........???

 

[Space cat]

If EDF have actually looked at your 80 amp rated CU and agreed to fit a 100 amp fuse then I suggest that the joke is on them.

 

[JohnD]

they don't care, it's not their responsibility.

What the fuse is, inside their 100A carrier, may be anything (mine is a 100A carrier, marked "fused 100A", but inside is a 60A cartridge.).

 

[Tonyx]

In fairness to EDF they didn't see the old CU when they agreed in principle to upgrade the main fuse to 100A. As it turned out they main fuse was actually 80A and I've just replaced the old Memera 3 CU with a 100A CU so all should be well for the upgrade and new shower.

Thanks for the imput guys.

Anthonyx