OK, so for the pumps or any other load that is basically just a motor, you need to use the nameplate HP rating and Table 430.248, not the nameplate amps. Then as usual you include the extra 25% of the largest motor on the entire feeder, which is presumably the 19A HVAC compressor, which is already included in its MCA.
Ok, got it. Thanks for cluing me into using the HP rating vs nameplate amps. I kind of get it and also seems to go against the grain of not using mfg amps
I'll make those updates.
So, on the one hand, if it has an electric griddle, maybe you should count it as a range, and then you are stuck with Column C? On the other hand, it's under 8.75 kW, so going with the row 2 Column A and Column B numbers is probably defensible. You're trying to get as low a number as is defensible, knowing that it will still be an overestimate as Article 220 is very conservative.
I believe I can defend it on a gas range, at a minimum not negligent. Yep, using the most conservative NEC approach, and then having things like dryers way over-spec'd and counting that mini-split, when it would never be used in the dead of winter, unless the boiler has a failure, not to mention some high current appliances and pumps rarely used.
That would be less of an issue than in a closet, and maybe whatever model you get will leak less humidity. Just a possibility to keep in mind, something I didn't expect of heat pump dryers.
It's good to know. Outside of the humidity issue, how do you like yours? And were you able to tie in to the washer drain? I haven't started to noodle that yet.
Not sure you want to thrown money at the issue, or that you have duct access to do so, but perhaps a spot HRV
like this could help manage that humidity issue.
I would think that any time you ask a manufacturer about a lug or termination in a piece of equipment, they would give you the rating as used in that piece of equipment, rather than in isolation on a shelf. But I wouldn't swear to it.
On the other hand, some other random guy on the Internet:
https://forums.mikeholt.com/threads/mllbank-meter-base.146953/
Cheers, Wayne
You would think they'd understand where you're coming from, but think he literally gave me the lug rating. "Me: Are the lugs on meter socket xyz 75C or 90C? Matt@Milbank: Hold on, I have one right here on my desk... it's a CU 9 AL, so that means it is a 90C rated lug".
There were a few other questions I didn't respond to previously:
If you have a receptacle dedicated to a built-in microwave (versus just a countertop microwave that if you removed it, its receptacle would look like all the other countertop receptacles), use the microwave nameplate data, not the 1500 SABC allowance.
I was going that way, but it looked to my benefit to consider it an incremental SABC. 1500VA x 0.35 vs 1200VA x .75, if I did that right. It's a microwave that is rated for either countertop or install, but going to sit on a shelf in a cabinet, with required clearances.
[Also, as an aside, it's odd the HVAC MCA of 42A is so much larger than 125% * 19A (compressor RLA) + the fans. Are the indoor units powered from the outdoor unit? How many do you have? I'm guessing that since the outdoor unit can support up to 8 indoor units, the difference is 8 times an allowance for the indoor units. If you have much less than 8, there's an argument for reducing the 42A figure, although that would be supported by the code language.]
Yes, the indoor units are powered directly from the outdoor unit. I have 5 indoor units. There may be a branch box that allows more, but they can only total a given number of BTUs. The head units draw almost nothing... they're a few fans and motors to sweep the louvers up/down/left/right
I had looked at this last year, and think that is why I went into the manual and aiming to consider the rated loads for one of the following conditions and had this note in my initial calc:
"MXZ-8C48NAHZ2: 3930w cooling, 6870w heating@17f, 7910w heating@5f. Heads total 3.2A actual. This totals max: 36.2A, but install manual calls for min ampacity of 42A. Note, if not considering heating, should be at 19.6A
Spec sheet rec. 45A breaker. Install manual says max OCPD = 50A".
I was initially thinking my 'worst case' would be the 36.2A. The branch box probably has a small load, too.
If you want the steam shower to have priority whenever it is used, and if the subordinate load has some contacts in its controls that would let you force it to stay off, then you can use a current sensing relay. It consists of a split CT that would go over one of the wires to the steam shower, and whenever the current in that wire is above a threshold level, that induces enough power in the relay itself to switch a pair of contacts. I have used these a couple times:
I like this idea. I had not gotten too deep into considering energy management yet, but just starting to poke around. I wasn't clear how accepting AHJ would be of 'custom/homegrown solutions' like this. Now, if you were having a PE stamp on your prior installs, no doubt, no issue. The nice thing about this one is the simplicity of the setup... it is more of the lockout you mentioned than energy management based on some sort of decision making. So I can see a reasonable case made for this, provided it can fail safe. I read through briefly, but need to dig closer to see if it is normally open / closed and if it's a simple dry contact or if some low voltage (say 24VDC) can pass through the response side of the device - do you know?
Last night I did glance at the span panels and the eaton smart breaker solutions, and on one hand I feel like I might be missing the boat going with old/dumb service equipment, but also knowing this is a rapidly evolving area that is about to explode with options. I just hate to come back later at the expense and effort and re-work a bunch of stuff for battery/generator/solar/etc, though the current options may not even fit my physical constraints (e.g. I have to use a trailer/ranch panel outside, and I can only use shorter panels in the garage and rental, with limited stud bay space).
All that said, I feel like with this massive residential service I have, I should be able to make just about anything work with a few tricks out of the bag.
Specifically (on your proposal), my true preference would be to have the steam shower lowest priority (very infrequent use, and if it doesn't turn on, someone can go figure out what needs to go off, but I honestly doubt that will materialize). But, what you propose is simpler, and could likely tie into the 24v controls for the electric heater. They're somewhat similar sized loads, so it wouldn't be a bad match up, and with the heater already having low voltage controls, it is a good marriage.
I think the appliances I have that are worth considering energy management on (for service and panel current management, but not solar/battery detailed management) are:
- Steam Shower
- EVSEs
- Electric Duct heater for makeup air
- Hot tub heater (there's a little more risk with this one in cold climate, though I would need to keep the circulation pump enabled and have some alerting if the temp dropped below a threshold).
- Possibly well pump, as it would mainly be used for irrigation
Alas, before I dive into that too far, I need to first know my capacity (is it 400A, 380A or 373A) and calculated loads. I also need to go run the optional calc for the service entrance conductors, as that should lower my combined current demand.