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Heat pump install overloads home fuse - 80A limitations

NJT · 2024-08-15T21:54:56Z

Evening all. I'm in the process of getting a heat pump installed. The initial surveyor put a tester on the mains inlet, while getting me to turn on fully electric shower, kettle, oven and the 2 biggest induction hobs. He stated it overloaded our 60A fuse, so I got the DNO to fit the biggest they could which was 80A, fitter didn't see a problem with what I told him we were proposing fitting. In the meanwhile I got a solar install with 5kw inverter. Didn't think there was a problem until octopus sent in a DNO request which they've refused as it exceeds our limit coming in at 92A, that's without the solar. Anyone else see a solution or had similar problems? I've emailed octopus but they don't always reply as soon as I'd like. Is the electrical test really just turn on fully all the highest powered appliances in the house at the same time, take a reading and pass or fail? Thanks

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NJT

(@njt)

Trusted Member Member

Joined: 2 years ago

Posts: 59

Topic starter 23/08/2024 5:09 pm

@old_scientist

I've had the DNO application back and they've passed it.

Taking out the 40A electric shower made it ok.

When I say take out, I just mean out the equation not physically off the wall, not yet anyway till heat pump is so up and running then I won't need it anyway so it'll be removed permanently .They just want it down on paper.

Still got solar, induction hob, double oven microwave and soon to be installed heat pump so it'll still be way up there.

But chatting to electrician says 80A will easily take 100A for a few hours anyway.

👍

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Old_Scientist

(@old_scientist)

Prominent Member Member

Joined: 2 years ago

Posts: 575

23/08/2024 10:10 pm

@njtt Great news that you've had it back approved. I found the DNO (NG in my case) were more than reasonable and very helpful.

Samsung 12kW gen6 ASHP with 50L volumiser and large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW). Net Zero

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NJT

(@njt)

Trusted Member Member

Joined: 2 years ago

Posts: 59

Topic starter 24/08/2024 4:34 am

@old_scientist

Yes NG for me too.

They even rang me up 2 days after application was sent in to say

"I thought you like to know it was accepted"

That's 2 dealings I've had on the phone with NG with upgrade to fuse and the heat pump and both very pleasant and quickly sorted.

👍

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Transparent

(@transparent)

Illustrious Member Moderator

Joined: 5 years ago

Posts: 3451

27/08/2024 1:59 pm

Posted by: @njt

↑

An 100A fuse would have made my life much easier.

I just applied to the DNO for a fuse upgrade as octopus after their heat pump survey said I needed one.

Getting in contact with the DNO was easy and fuse upgraded within days for free but stated their policy will only allow up to 80A fuse.

As I've already mentioned they removed neighbours 100A fuse and replaced it with an 80A

I've just addressed this issue here in the topic DIY solar upgrade.

I've spoken with the senior NGED engineer who issues their operational specifications and represents their interest at the Electricity Networks Association.
He's friendly, helpful... and deeply knowledgeable.

When he says they need to downgrade to 80A Service Fuses, then he won't have done that lightly.

As others here have pointed out, a Service Fuse is a very long time-delay device!
You can draw 100A through it for maybe an hour before it gives out.

A high proportion of homes which need to draw more than 80A (19kW) have inefficiencies within them which really ought to be addressed!

Yes, an electric shower is a very high demand appliance... more so than an EV charger.
And there's a lot of them in houses which have had additional loft insulation installed by morons on top of the electrical supply cable!

Let's hope that the need to downgrade to an 80A Service Fuse will cause more home-owners to re-evaluate their 10kW electric shower !

Let me end with a photograph showing 'loft flooring' which has been done properly:

A shows the original ceiling joists.
The span length is 4.6m, so these old 3-inch deep timbers aren't capable of taking the new floor.

B are the new floor joists which have been placed alongside the ceiling joists.

That leaves plenty of space below the new chipboard floor (C) for insulation,
and the re-routing of power cables (2.5mm² and larger) above the insulation layer.

Save energy... recycle electrons!

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NJT

(@njt)

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Posts: 59

Topic starter 27/08/2024 2:13 pm

@transparent

Very informative.

Thank you

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IanMK13

(@ianmk13)

Reputable Member Member

Joined: 4 years ago

Posts: 195

27/08/2024 4:53 pm

@transparent A concern of mine regarding the ability of an 80A fuse to carry in excess of 100A for a significant time is that if this is done regularly the fuse could deteriorate over a period of time and eventually fail (you might say this wouldn't be a bad thing).

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