3ph to domestic property, 80A or 100A?

[RutlandFox]

Customer has asked for DB and new CUs for large dwelling house, WPD are putting in 3 phase to replace 100A single phase and are saying fit 80A main fuses....

Main load on all phases is Tesla wall charger 32A and a ground source heat pump 32A.

Given they are both loads that will run potentially continuous duty cycle, that's 64A, leaving 16A headroom per phase.

There are 2 CUs one with 3 RMs and one for a bunch of lighting circuits. Presuming I wire each CU to a separate phase, that's still not going to be enough unless WPD put in 100A main fuses?

Options, please!

1) Leave the existing 100A single phase in and have 2 meters?
2) Insist they install 100A supply/fuses? That's still only a 36A supply after the two big loads.
3) Split the RM CU and have different floors on different phases? Maybe even add a 3rd CU on L3?

Thx!

 

[davesparks]

What is the actual load before the upgrade?
Has it been measured via a load study?

What size supply did you apply for from WPD?

 

[pc1966]

There are 2 CUs one with 3 RMs and one for a bunch of lighting circuits. Presuming I wire each CU to a separate phase, that's still not going to be enough unless WPD put in 100A main fuses?

Is it the 3 RM that you are concerned by? The On Site Guide Appendix A table from domestic final circuts has 100% of the largest circuit + 40% of the remainder, say, 32 + 0.4*(2*32 + 3*6) = 65A

 

[davesparks]

Is it the 3 RM that you are concerned by? The On Site Guide Appendix A table from domestic final circuts has 100% of the largest circuit + 40% of the remainder, say, 32 + 0.4*(2*32 + 3*6) = 65A

65A load for a domestic house? Only if they're growing weed!

 

[pc1966]

65A load for a domestic house? Only if they're growing weed!

True, it seems way too high for any sane activity, but in terms of diversity versus total listed CU circuits it is at least justifiable!
[automerge]1588004200[/automerge]
Actually the lighting should be separate and have a 0.66 factor.
3 RM & 3 lights = 32 + 0.4 * (2*32) + 0.66*(3*6) = 69A and still higher than sane!
But better than 114A

 

[plugsandsparks]

I think its std practice for WP, they tried it on me after paying for a new pole TX. I "demanded" a 70KVA supply, it did the trick...

 

[James]

is the heat pump existing?
if not, I would suggest a 3phase unit.

can you put in a 3 phase db adj. meter with a feed out to each of the house db's and separate feeds to the big loads (charger and heating etc.)

this will alow you to balance the phase currents as best you can.

 

[davesparks]

True, it seems way too high for any sane activity, but in terms of diversity versus total listed CU circuits it is at least justifiable!
[automerge]1588004200[/automerge]
Actually the lighting should be separate and have a 0.66 factor.
3 RM & 3 lights = 32 + 0.4 * (2*32) + 0.66*(3*6) = 69A and still higher than sane!
But better than 114A

How

is the heat pump existing?
if not, I would suggest a 3phase unit.

can you put in a 3 phase db adj. meter with a feed out to each of the house db's and separate feeds to the big loads (charger and heating etc.)

this will alow you to balance the phase currents as best you can.

Acvpridng to the OP it is a three phase car charger and a 3 phase heat pump

 

[RutlandFox]

Yes the ev charger and heat pump are both new install and both 3ph.

 

[stevels4]

Whole current meters generally have a maximum current limitation of 80A per phase, fitting 100A cut out fuses would exceed that unless you are using CT metering.