Fixed space heating max demand
Fixed space heating max demand
I have a new build where the customer has chosen 13 infrared ceiling mount heaters for their heat source. The heaters vary in size from 350-900w and total 10.5kw. They connect by a ceiling mounted 10a socket. My question, should my max demand calculation allow for these? It is not a singular, fixed space heating rated at more than 10a, but when they are all considered they are definitely more than 10a. Allowing for them takes my max demand calc from 46a to around 76a. This would mean installing a 100amp supply and running mains (about 70m) accordingly. Thanks
Re: Fixed space heating max demand
you have plenty of choice about how you determine MD [2.2.2].
Whatever you decide it us; you then select cable size to carry it; and you protect that cable against overcurrent.
Which is essentially determining MD by "limitation".
Therefore MD is not an (electrical) safety consideration; so the point is to minimise inconvenience from unwanted tripping.
In particular, you don't want the supply fuse to operate due to overload.
If you are following Table C1 (domestic); then technically none of them are "sockets > 10A for the connection of ... fixed space heating equipment" (Row D). So they can be treated as normal sockets (Row B1).
As such, assuming there are at least 20 other sockets as GPOs; then the 13 of them are assessed as 5A;
rather than 10.5 kW = approx 46 A; x 75% = 34 A.
On the other hand; if they were directly connected instead; then they certainly would be Row D;
Probably OK for domestic, as the chances of all being used at same time are small.
Different in a non-domestic situation; where all (or most) used together might be typical, even if infrequent.
You don't have to use the assessment guide in App C.
So instead of choosing one extreme or the other; why not assess their contribution as somewhere between?
What you want to avoid of the supply fuse ever operation due to overload.
Even more, you don't want to have to upgrade mains.
Consider a 63 A supply, but with mains cable for 100A .
That way, if the fuse blows the cable is already on place and changing to a higher supply capacity will be less of a problem.
Another option might be multi-phase supply; 1 x 63A now but cable in place for 2 x 63A.
Whatever you decide it us; you then select cable size to carry it; and you protect that cable against overcurrent.
Which is essentially determining MD by "limitation".
Therefore MD is not an (electrical) safety consideration; so the point is to minimise inconvenience from unwanted tripping.
In particular, you don't want the supply fuse to operate due to overload.
If you are following Table C1 (domestic); then technically none of them are "sockets > 10A for the connection of ... fixed space heating equipment" (Row D). So they can be treated as normal sockets (Row B1).
As such, assuming there are at least 20 other sockets as GPOs; then the 13 of them are assessed as 5A;
rather than 10.5 kW = approx 46 A; x 75% = 34 A.
On the other hand; if they were directly connected instead; then they certainly would be Row D;
Probably OK for domestic, as the chances of all being used at same time are small.
Different in a non-domestic situation; where all (or most) used together might be typical, even if infrequent.
You don't have to use the assessment guide in App C.
So instead of choosing one extreme or the other; why not assess their contribution as somewhere between?
What you want to avoid of the supply fuse ever operation due to overload.
Even more, you don't want to have to upgrade mains.
Consider a 63 A supply, but with mains cable for 100A .
That way, if the fuse blows the cable is already on place and changing to a higher supply capacity will be less of a problem.
Another option might be multi-phase supply; 1 x 63A now but cable in place for 2 x 63A.