Maximum Demand / ENA / EV Help!

D4G:..

I can hear the arguments now ?

....

The whole debate came from trying to work out what figure to put on the ENA form....


Even if I disconnect the older shower, that leaves:

36A shower

17A cooker after diversity

32A EV

Theres 85A without a kettle, tumble dryer, lights .......

The house cut out fuse will be something like the ones above. Run your finger along the 60A, or if you prefer the 80A curve, until it intersects the current you think your showers plus house loads may draw,  and read off the time to failure on the left hand side.

In practice it will simply never fail before the shower user is dressed and ready to go out for the evening. I agree its not a nice thing to rely on, and if the cooker was being used on all rings at the same time  as both showers for several folk in rapid succession, (guests at Christmas is a classic) then it might just fall over.

It's not really right to rely on this allowance of course, but remember an xx fuse is designed to carry xxA for ever, and several times that for short periods.

Luckily the time constant for the house wiring, and the company supply cables for that matter, to heat up and melt is even longer, so the fuse generally performs its protective function just fine.

Pans of water boil and cooking of vegs is almost done within 15-20mins (~ 1 kilosecond on that graph) and the ring gets turned down from max long before that. Similarly a long shower is probably 10-15 mins of actual showering and a lot of faffing about before and after.

A car is a different situation altogether as it may be tens of kiloseconds.

I hope we can see why it has not blown the existing fuse yet.

Mike

D4G:..

I can hear the arguments now ?

....

The whole debate came from trying to work out what figure to put on the ENA form....


Even if I disconnect the older shower, that leaves:

36A shower

17A cooker after diversity

32A EV

Theres 85A without a kettle, tumble dryer, lights .......

The house cut out fuse will be something like the ones above. Run your finger along the 60A, or if you prefer the 80A curve, until it intersects the current you think your showers plus house loads may draw,  and read off the time to failure on the left hand side.

In practice it will simply never fail before the shower user is dressed and ready to go out for the evening. I agree its not a nice thing to rely on, and if the cooker was being used on all rings at the same time  as both showers for several folk in rapid succession, (guests at Christmas is a classic) then it might just fall over.

It's not really right to rely on this allowance of course, but remember an xx fuse is designed to carry xxA for ever, and several times that for short periods.

Luckily the time constant for the house wiring, and the company supply cables for that matter, to heat up and melt is even longer, so the fuse generally performs its protective function just fine.

Pans of water boil and cooking of vegs is almost done within 15-20mins (~ 1 kilosecond on that graph) and the ring gets turned down from max long before that. Similarly a long shower is probably 10-15 mins of actual showering and a lot of faffing about before and after.

A car is a different situation altogether as it may be tens of kiloseconds.

I hope we can see why it has not blown the existing fuse yet.

Mike