total load

[Treg the electrician]

residential... I have a 200 amp panel and some hvac equipment going in downstream. 15 kw strip heat 60/30 and a heat pump 25 amps . I plan to install 100 amp sub panel . what is a good calculation to determine if 100 amps is enough.

 

[ptonsparky]

Roughly:
15000/240=62.5
62.5+25=87.5

What do you think?

 

[Treg the electrician]

that seems right to me but im just wondering since they all wont be running at the same time if i could dial that down and get below 70 amps

 

[ptonsparky]

that seems right to me but im just wondering since they all wont be running at the same time if i could dial that down and get below 70 amps

Depends on the HP set up. They may run at the same time.

 

[Treg the electrician]

is there a calculation that takes that into account ? like a nominal % or something like that i know it probably seems like a dumb question but i am used to other people making these decisions for me and now im in a position where i have to figure this stuff out and its a learning curve for sure .

 

[ptonsparky]

1.25*62.5=78 plus the 25 gives you 103.
Take a close look at the HP label. That 25 may be the MCA, which means the actual load is closer to 20.

Details.

 

[Treg the electrician]

Depends on the HP set up. They may run at the same time

yes that 25a was mocp the mca was 20 that puts me at 98. just within the margin thank you for the help . do we always multiply by 1.25 ?

 

[James L]

If it were me, I'd see about having the controls rewired.

15kw is a 10 + 5

They function as auxiliary or emergency

Auxiliary is designed to assist your heat pump when heat pump is not quite adequate.

Emergency is manually selected when heat pump is not working at all.

Imo, 10kw is likely enough for auxiliary.
Use 15kw for emergency.

In that scenario your 5kw would never run at the same time as the heat pump.

I'd run this scenario past the HVAC tech, see if it's doable

 

[infinity]

yes that 25a was mocp the mca was 20 that puts me at 98. just within the margin thank you for the help . do we always multiply by 1.25 ?

Can you post a photo of the thr nameplate? MCA of 20 is likely drawing a little more than 15 amps.