National Grid fuse upgrade to 80A

FreeBear

Netexporter said:

I tried for a 100A fuse, but got an 80A, because the new consumer unit has 100A breaker, but I now realise that it isn't necessary. If the transient load did exceed 100A then the breaker would deal with it, long before the company fuse was in any danger.

The breaker (that big red switch) in your consumer unit will not provide any protection against transient loads. The 100A rating just refers to the maximum current that should pass through it. Pull 150A or 200A, and it will probably get hot and may even melt if the current draw is sustained, but it will not stop the current flowing.

NedS

An update - after going back and forth with NG for a few days (they insisted I complete the form), they have now agreed that we need upgrading to an 80A fuse and have referred it to the local team. It wasn't an easy process, but to NG's credit they were excellent in their communication throughout, by both email and phone calls, always responding quickly and always moving the process forward.

The Maximum Demand of the heat pump was an interesting topic - it's a 12kW Samsung unit, and in the ENA heat pump database, it's listed as 6.44kW (28A)*, and there is also a 3kW (13A) immersion fitted which could be used simultaneously (if the user selects the DHW Boost facility), so the combined Maximum Demand was adjudged 41A.

Because the total heat pump maximum demand is greater that 32A, it should not have been installed without prior permission from the DNO. NG have graciously agreed to upgrade the fuse and issue a permission letter. I wonder how many heat pump installs fall into the category of mine where the DNO has not been notified, and installation may have required prior permissions.

[*] From Samsung's own specs, the ASHP can draw 6.44kW when heating DHW (requiring 55C flow temps) when it's -5C outside.

Reed_Richards

You, or your installer, is obliged to notify the DNO when you have a heat pump installed.  If the new maximum demand exceeds 60 A you are obliged to seek prior permission.  I'm not aware that 32 A has anything to do with this.  

NedS

Reed_Richards said:

You, or your installer, is obliged to notify the DNO when you have a heat pump installed.  If the new maximum demand exceeds 60 A you are obliged to seek prior permission.  I'm not aware that 32 A has anything to do with this.  

On the NG EV/ASHP notification form, to fall under install and notify the maximum demand of the ASHP must also be less than 32A. If it's over, then it falls under seek permission prior to install.

There was some debate if the immersion (13A) should be included within this figure or not, as the ASHP alone is rated at 28A.

Either way, Maximum Demand is also over 60A and permission should have been sought before installation. I was unaware of this and the installer omitted to mention it and went ahead with the installation, and has not notified the DNO of the installation (which I have now done).

Reed_Richards

Bad installer!  In my case my immersion heater had its own circuit and I had an immersion heater (in a different cylinder) before the heat pump was installed.  In your case it is academic since the DNO was not informed pre or post installation.  Was the installation MCS certified?  I can't believe that the certification allows an installer to get away without the necessary DNO notification.

NedS

Yes, installer MCS certified, and installation carried out under ECO4 Scheme. The solar installer didn't notify the DNO either, so this seems to be a common theme.

The immersion is on a separate breaker to the ASHP, BTW.