Main fuse protection

[Bagendman]

In our house the main fuse is rated at 100A maximum. The individual circuits in the consumer unit, if all used simultanuously, add up to much more than 100A. Now I understand this is common practice as it is assumed that not all circuits will be used to their max at the same time (the diversity principle). The question is though, what if they are ? For example, there could be a shower (10KW=42A), cooker (30A if all hobs and both ovens on at once), 4 electric heaters (each 2KW) =30A total) + lighting, Water heater 13A, TV, fridge etc (say 3A). This easily exceeds the 100A. Although, I understand the diversity principle, it seems to me that the liklehood of this happening is not so remote.

So if we did exceed the 100A, I assume the main supply fuse would blow. Does this mean that the power company would have to be called out to replace the fuse or do they reset themselves automatically? Calling out the power company would likely take a while, so we'd be left with no power. Why is it that there is not a quick reset fuse inside the consumer unit, to make sure that the maximum power taken never exceeds the main supply fuse rating? This would seem to be a simple thing which all houses should have. Does anyone know why this does not exist ?

 

[rogerdean]

A cheaper option than have a 3ph supply installed might be installing a load shedding relay that will isolate heavy loads if total gets near 100A.

That's really helpful, thank you! I have set up something like this via my home automation setup - right now if it goes above 22kw then some of the storage heater are turned off. But it's a system that relies on the WiFi behaving so your suggestion is really welcome...

 

[Avo Mk8]

Not to encourage ignoring overload, but the fuse characteristics indicate that a 100A fuse won't blow until sustained current reaches around 130 - 140A. (I guess there's a specific minimum value in the standard, but I don't know what it is!)

 

[rogerdean]

A cheaper option than have a 3ph supply installed might be installing a load shedding relay that will isolate heavy loads if total gets near 100A.

Is there such a thing as a relay controlled by a CT clamp? So a device could be disconnected based on the overall draw? Can't find one but don't know what the right name would be. Thanks again

 

[Mike Johnson]

As DefyG said, it's a load shedding relay, I don't know if they are available in the UK, but in the EU they are available as multiple units that will switch off loads in progression if required to maintain the load below the incoming supply.

 

[nicebutdim]

As DefyG said, it's a load shedding relay, I don't know if they are available in the UK, but in the EU they are available as multiple units that will switch off loads in progression if required to maintain the load below the incoming supply.

Should be Garo units available in the UK. It seems their products have been adopted by quite a few wholesalers since their shower priority board came in for some demand.

 

[rogerdean]

As DefyG said, it's a load shedding relay, I don't know if they are available in the UK, but in the EU they are available as multiple units that will switch off loads in progression if required to maintain the load below the incoming supply.

Thanks Mike, that's what I need. Only things I could find seem just to monitor another single circuit rather than the overall load. A link would be brill if you can... Thanks

 

[rogerdean]

Thanks Mike, that's what I need. Only things I could find seem just to monitor another single circuit rather than the overall load. A link would be brill if you can... Thanks

Thanks for the support folks. Turns out the best way for me is simply to upgrade my EV charger to one that has load management built in, like the Zappi or newer Ohme. Talk about making it complicated for myself eh?

 

[DefyG]

The Schneider A9C15908 is another, not cheap at £500 ish

Available at UK wholesalers (Edmundson & Yesss) but link to;

A9C15908 | Schneider Electric iC60 Series Contactor, 230 V ac Coil, 1-Pole, 90 A, 230 V ac | RS

uk.rs-online.com

 

[Avo Mk8]

Is there such a thing as a relay controlled by a CT clamp? So a device could be disconnected based on the overall draw? Can't find one but don't know what the right name would be. Thanks again

Yes.
Google something like "split core ct current monitoring relay 100A"
This one has the disadvantage you have to feed the tail you're measuring through the hole. You really need a split core version:

https://docs.rs-online.com/5d25/0900766b813e168e.pdf

Came across this, which when set up to the current you want (say 100A) could switch a relay or contactor in part of your installation:

CS-625 AC Current Switch (high output)

Measurement Systems provides CS-625 AC Current Switch (high output) for your business

www.measurementsystems.co.uk

But sounds like you won't need it now