Main Breaker Rating?

[iggy2]

Hello all - I have the following loads (VA) entered into our spreadsheet for a 208v, 1 phase service/feeder calc for an EXISTING dwelling unit (apartment) where the FPE loadcenters are being replaced:
1,476 (492 sq. ft at 3 VA/sq. ft)
1,500 (small appl. B/c - only 1 existing)
8,000 (electric range)
131 (hood fan/light)
4,000 (electric water heater)
6,375 (electric heat, baseboard)
(No laundry, bath EF, disposal, D/W, etc.)

20,842 (total after gen ltg & small appl., and 'other loads' at 75% demands taken)

divided by 208V 1 phase = 100 amperes.

Question is - what should the main breaker in the apartment loadcenter be? 100A? Or do some/any of these loads have to be considered continuous? And if so, do I have to add 25% of those loads per 215.3??? (i.e. is the loadcenter buss a 'feeder' per definitions?)

(Existing main CB is 125 amps - but Eaton cannot supply a UL listed retrofit kit for this box with a 125A main - they need the main to be 100A or less to fit in this existing, tiny FPE box. I assume due to wire bending space.)

Thanks.

 

[petersonra]

Does the PB in the aprtment itself even need a main cb?

 

[iggy2]

yes.

 

[augie47]

Keeping in mind the NEC is minimum required.
If the load calculation is 100 amps then a 100 amp would be all that is needed.
Certain branch circuits such as water heater & heat are required to be considered continuous but I don't believe this carried over to your load calculations.
I disagree that the panel is required to have a main as far as the Code is concerned IF there is an accessible main ahead of the panel.

 

[dana1028]

loads

loads

Doesn't Col. B of Table 220.55 indicate you only have to calc 80% of a household electric range rated 3.5 kW thru 8.75 kW?....thus your 8 kW would be calc'd at 6.4 kw.

 

[iggy2]

Doesn't Col. B of Table 220.55 indicate you only have to calc 80% of a household electric range rated 3.5 kW thru 8.75 kW?....thus your 8 kW would be calc'd at 6.4 kw.

Perhaps, but I am only concerned about main CB rating, with given info.

Certain branch circuits such as water heater & heat are required to be considered continuous

Code reference??? Since EBB and WH are thermostatically controlled, I would think they would cycle on/off....Also see 220.15 - electric space heating to be carried at 100%. (220.15 reference is from 2002 NEC - I do not have 2011 here at home...)

I disagree that the panel is required to have a main as far as the Code is concerned IF there is an accessible main ahead of the panel.

panel is fed by a tapped riser, protected by a 200 A feeder breaker, which does not happen to be accessible to the occupants (although it is under management, but not 24 hr on-site management).

Thanks.

 

[iggy2]

I also note that none of the dwelling unit examples seem to take continuous vs. non-continuous loads into account. They add up the loads and divide by voltage, as I have done.

 

[jumper]

Code reference??? Since EBB and WH are thermostatically controlled, I would think they would cycle on/off....Also see 220.15 - electric space heating to be carried at 100%.

Thanks.

422.13 Storage-Type Water Heaters. A fixed storagetype
water heater that has a capacity of 450 L (120 gal) or
less shall be considered a continuous load for the purposes
of sizing branch circuits.

424.3(B) Branch-Circuit Sizing. Fixed electric space-heating
equipment shall be considered continuous load

 

[augie47]

Derek answered your first question, and your explanation shows why you do need a MB panel.

Other than it meeting only minimum standards, I see no reason the 100 am p would not work.

 

[iggy2]

422.13 Storage-Type Water Heaters. A fixed storagetype
water heater that has a capacity of 450 L (120 gal) or
less shall be considered a continuous load for the purposes
of sizing branch circuits.

424.3(B) Branch-Circuit Sizing. Fixed electric space-heating
equipment shall be considered continuous load

Thank you for the references. These are both related to branch circuit rating though, so presumably would not apply to the panelboard main circuit breaker, which is sized as a feeder.