The Mother of all Story Problems

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If that '40W' light stays on continuously rather than getting switched with the opener, then it could add up to real money.

If the electronics draws even 10W sitting their waiting for the control signals, then that low level continuous usage would swamp the numbers calculated so far.

-Jon
 
Besoeker said:
That would infer that the motor is has a efficiency of just 33% and unity power factor. Neither is likely to be correct.
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It would not infer that, but it might imply that. ;)

Actually, my perspective is that we don't need to know anything about efficiency or power factor. The NEC has a table that tells us what values of current to use, when performing load calculations that involve motors. If we simply pull the value off that table, nobody can question our basis for that calculation.
 
charlie b said:

It would not infer that, but it might imply that. ;)

Actually, my perspective is that we don't need to know anything about efficiency or power factor. The NEC has a table that tells us what values of current to use, when performing load calculations that involve motors. If we simply pull the value off that table, nobody can question our basis for that calculation.
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Quite.
But energy cost for domestic consumers is for kWh, not current. Poor PF for the same kW is more current but no greater cost (other than losses in conductors).
 
On the one hand, assuming the opener is for common space, it shouldn't be on the tenant's meter.

On the other hand, I'd hand the tenant a $20 and tell them to be done with it. (And to bill me if they think it's more. With the figures.)
 
I think that in MN on old duplexes with the common lights on one of the apartment panels it is legal still as long as you spell out in the lease what you are paying for. I'd have to find a reference for that if anyone cares. Don't use it as legal advice either as right now it's just something I have heard.
 
Wow.

3 pages of posts on how much electricity a GDO uses in a year. Just goes to show you, this forum can beat any topic to death and then get completely sidetracked too.:wink:
 
zbang said:
On the one hand, assuming the opener is for common space, it shouldn't be on the tenant's meter.

On the other hand, I'd hand the tenant a $20 and tell them to be done with it. (And to bill me if they think it's more. With the figures.)
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Are those garage door openers are connected by a cord? If so couldn't the landlord at any time run in there and use that power to run a table saw or an air compressor? That would change things a bit especially if the landlord knows where to get free power.
 
Install a solar panel, battery and inverter. Makes it totally independent of the tennant, No minimum meter charge, feud is over. You make money installing the solar panel and equipment.
 
Besoeker said:
But energy cost for domestic consumers is for kWh, not current. Poor PF for the same kW is more current but no greater cost (other than losses in conductors).
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My point is that I believe the authors of the NEC took efficiency and power factor into account, when they gave us the values in Tables 430.248 and 430.250. So I can take a value of current from the table, multiply by the voltage at the top of the column, multiply by the square root of the number of phases ;), and treat the answer as the VA load of the motor, without thinking about any other considerations.
 
charlie b said:

My point is that I believe the authors of the NEC took efficiency and power factor into account, when they gave us the values in Tables 430.248 and 430.250. So I can take a value of current from the table, multiply by the voltage at the top of the column, multiply by the square root of the number of phases ;), and treat the answer as the VA load of the motor, without thinking about any other considerations.
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Yes, I agree. VA. Or kVA - but not kW. Thus, you can't use just the current to calculate the input power to the motor nor its operating energy costs if you pay for kWh.
 
Thanks to all for the replies and opinions regarding this thread. My customer is being taken to small claims and this was one of the former tenants issues. I'd love to be at the hearing when the judge realizes how frivolous this area of the dispute is:cool:. It was kind of eye opening for me too as I never imagined a garage door opener was so economical to operate.....Now I'll run it up and down at will instead of leaving it open all day:D
 
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