Generator feeder questions

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Well, we bored the hole through the steps today, using my Bosch SDS-Max rotary hammer with an SDS-Max-lok coupler and an extension shaft. Yep, solid concrete all the way through. :roll: The good part is that the PVC slid right through, although I covered the end with duct tape to keep it empty of dust and debris.

We also mounted the ATS to the wall with a nipple with lock-nuts and plastic bushings. The #8 cu EGC will pass though from main disco to ATS. No need to bond the nipple itself, since it's not part of the service pathway, right?

New questions: since I won't be interrupting the existing neutral in/neutral out connection in the main disco, the neutral in the nipple between the ATS and the main disco only needs to be the size of the generator feed neutral, right?

Plus, since five of the main disco's six neutral terminals are in use (neutral in, neutral out, EGC out, and two GECs), is it okay to land the ATS/generator's EGC on a lug bolted to the main disco's enclosure, as long as the bonding screw is in place?

Added: Where do I get one foot of 1" non-metallic flex? I want to put it in to minimize vibration transmission.
 
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I'm still trying to figure out how your using a generator with a 70 amp output breaker to feed what seems to be a 200 amp service through an automatic transfer switch with evidently no load shed capabilities.

but I may not know the whole story.

JAP>
 
What am I missing? (I'm really asking) There is no air-conditioning, and the heat is oil-fired. The panel has maybe 10 breakers in it.

The ATS has a four-circuit module in it, but I'm not aware of anything that can or should be shut down. Please advise me.
 
Generac ATSs do have load shed capability iirc. And the generator is sized by the load not the service.

I have lamented before how difficult it is to load a 20kW-plus resi generator to full load/overload. You usually have to *REALLY * try. Tho a load calc may exceed its rating, real world shows different. And if you used 60 plus amps continually, your electric bill would be enormous (rough math tells me 1k/month @ .10$/kw-hr ).

A supply house should have the 1 inch liquid tight flexible nonmetallic conduit
 
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JFletcher said:
Generac ATSs do have load shed capability iirc. And the generator is sized by the load not the service.

I have lamented before how difficult it is to load a 20kW-plus resi generator to full load/overload. You usually have to *REALLY * try. Tho a load calc may exceed its rating, real world shows different. And if you used 60 plus amps continually, your electric bill would be enormous (rough math tells me 1k/month @ .10$/kw-hr ).

A supply house should have the 1 inch liquid tight flexible nonmetallic conduit
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That's all well and fine when computing for a "Manual" Xfr switch installation where you backing the whole service.

I think it differs with an "Automatic" Transfer Switch installation unless your feeding an Emergency subpanel with a definite critical load only.

JAP>
 
I cant recall but I think when you use an "Autotmatic" transfer switch different rules apply.


JAP>
 
If he doesn't have load shed installed then I would think this install would be a violation of 702.4 (B) (2) (a).

JAP>
 
Can't the "full load" being transferred be determined by the 220.87(1) Ex, that figures out the highest average kW over 15 minute period for a min of 30 days?

Not exactly sure how you go about getting this number without some expensive monitoring equipment set up for that 30-day period...?

Is there a way to look at the historical poco bills to determine the highest kW/h?
I know my monthly bill graphs out the last 12 month kW/h for each month, telling me which month is my highest usage. Could you just divide by # of hours in that month to give you your average kW for that month?

My bill shows me in February I used 1,590 kW/h. Dividing that out shows me my average hourly kW usage for the whole month was 2.35 kW. So a 5kw generator with an ATS setup would be more than enough to satisfy my needs.

I understand there might be "peaks" where I temporarily might use more than 5kw of power, but I would assume worst case scenario, if it lasts longer than a few minutes, is that you trip the generators breaker?

Please keep this load Calc/generator sizing conversation going, I need to learn more about this topic!
Thanks!
 
sw_ross said:
Can't the "full load" being transferred be determined by the 220.87(1) Ex, that figures out the highest average kW over 15 minute period for a min of 30 days?

Not exactly sure how you go about getting this number without some expensive monitoring equipment set up for that 30-day period...?

Is there a way to look at the historical poco bills to determine the highest kW/h?
I know my monthly bill graphs out the last 12 month kW/h for each month, telling me which month is my highest usage. Could you just divide by # of hours in that month to give you your average kW for that month?

My bill shows me in February I used 1,590 kW/h. Dividing that out shows me my average hourly kW usage for the whole month was 2.35 kW. So a 5kw generator with an ATS setup would be more than enough to satisfy my needs.

I understand there might be "peaks" where I temporarily might use more than 5kw of power, but I would assume worst case scenario, if it lasts longer than a few minutes, is that you trip the generators breaker?

Please keep this load Calc/generator sizing conversation going, I need to learn more about this topic!
Thanks!
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The rule for the automatic transfer switch is based on "Full Load" and mentions nothing about "Calculated load".

JAP>
 
jap said:
The rule for the automatic transfer switch is based on "Full Load" and mentions nothing about "Calculated load".

JAP>
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To size a standby generator I do a service size calculation. I don’t count any loads that are large and easily shed through relays such as electric dryers, ovens, hot tubs, etc. The central AC can be switched through dry contacts in the ATS. Once these loads are taken out of the calculation it results in a small load for the generator to power.

A normal situation I find would be a house with a 100 amp Service that gets an 11kw generator and a service rated ATS. The Service size calculation might be 80 amps but the AC and the dryer are load shed making the revised calculation more like 40 amps. In reality the ac and the dryer will work most of the time unless the generator starts to strain. The same theory applies to a house with a 200 amp Service. 22kw gen, 200 amp ATS. Load shed two AC’s, dryer, oven, hot tub, etc.
 
sw_ross said:
Can't the "full load" being transferred be determined by the 220.87(1) Ex, that figures out the highest average kW over 15 minute period for a min of 30 days?

Not exactly sure how you go about getting this number without some expensive monitoring equipment set up for that 30-day period...?

Is there a way to look at the historical poco bills to determine the highest kW/h?
I know my monthly bill graphs out the last 12 month kW/h for each month, telling me which month is my highest usage. Could you just divide by # of hours in that month to give you your average kW for that month?

My bill shows me in February I used 1,590 kW/h. Dividing that out shows me my average hourly kW usage for the whole month was 2.35 kW. So a 5kw generator with an ATS setup would be more than enough to satisfy my needs.

I understand there might be "peaks" where I temporarily might use more than 5kw of power, but I would assume worst case scenario, if it lasts longer than a few minutes, is that you trip the generators breaker?

Please keep this load Calc/generator sizing conversation going, I need to learn more about this topic!
Thanks!
Click to expand...

A 5kw generator is only good for 20 amps per leg. It will not run any of your 240-volt loads, especially ones with a high inrush current, like your air conditioner. You Average 2.35 kilowatts, however momentary Peaks maybe 60 amps or higher, or 15 kilowatts. You might run your dryer for 1 hour every 2 or 3 days, your water heater May cycle on for 5 minutes every 2 hours, or may run continuously while you're taking a hot shower. All of these loads draw a fair amount of power, it's just that they don't run all the time so that your average energy use over 24 hours is fairly low. Your meter may almost come to a complete stop at night time with all the lights off AC off, no one using hot water, no one cooking, etcetera.

In the morning (especially a cold one) with people getting ready for work, taking showers (baseboard heat blasted) cooking breakfast, running hair dryers, blenders, toasters, coffee pots and so on, you could easily see 100 + amps if you were to put an amp clamp around the mains. Same in the evening with cooking dinner, dishwasher running, water heater running, dryer running, heat back on, and so on.

in the event that you overload the generator, it's simply going to shut down or trip its breaker.

it's interesting to note, or scary, depending on how you look at it, that the wires coming off of the stator on a 16 to 24 kW Generac are only 10 gauge. Two neutrals and two Hots, the latter of which are going to a 70-100 amp breaker
 
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JFletcher said:
....In the morning (especially a cold one) with people getting ready for work, taking showers (baseboard heat blasted) cooking breakfast, running hair dryers, blenders, toasters, coffee pots and so on, you could easily see 100 + amps if you were to put an amp clamp around the mains. Same in the evening with cooking dinner, dishwasher running, water heater running, dryer running, heat back on, and so on.
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First of all, who does that on a day when the power is out? Second of all, unless there is a huge amount of electric heat you'd be more likely to a two headed cow than see a house pull 100A.
 
ActionDave said:
First of all, who does that on a day when the power is out? Second of all, unless there is a huge amount of electric heat you'd be more likely to a two headed cow than see a house pull 100A.
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I was referring to normal conditions when Poco power is available.

And you're correct, and like I wrote earlier, it is extremely difficult to load a 24 KW generator to its maximum. The one time we did it, we turned on the air conditioner, the dryer, turned on the hot water so the water heater would come on, put a bowl of water in the microwave for 10 minutes, turn on the garbage disposal, turned on the oven, turned on all four burners on the stove, plugged in a hair dryer in the bathroom and left that running on high, and a few other things that escaped my memory. Even with all of that I believe we were only around 90 amps
 
Again, this house has no AC, and dryers use centrifugal switches, so they won't restart after a power failure.

Also, we're still on the 2011 NEC. Is that sizing rule in effect here?
 
JFletcher said:
momentary Peaks maybe 60 amps or higher, or 15 kilowatts. You might run your dryer for 1 hour every 2 or 3 days, your water heater May cycle on for 5 minutes every 2 hours, or may run continuously while you're taking a hot shower. All of these loads draw a fair amount of power, it's just that they don't run all the time so that your average energy use over 24 hours is fairly low. Your meter may almost come to a complete stop at night time with all the lights off AC off, no one using hot water, no one cooking, etcetera.

In the morning (especially a cold one) with people getting ready for work, taking showers (baseboard heat blasted) cooking breakfast, running hair dryers, blenders, toasters, coffee pots and so on, you could easily see 100 + amps if you were to put an amp clamp around the mains. Same in the evening with cooking dinner, dishwasher running, water heater running, dryer running, heat back on, and so on.
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All that definitely make sense! And makes me understand why you can't just go by the average usage!

I have more questions, but don't want to hijack this thread.
I'll either use search options or start a new thread.
Thanks!
 
The customer on this job lives alone, and is handicapped. He basically lives in front of his computer. His power usage is that of a shed.

It almost seems my questions are being ignored, and I started this thread. :? Please go over my last few posts to put together the facts.

I don't mind the sizing questions and answers, but I would like my questions addressed, too, like whether the disco/ATS nipple requires bonding.
 
LarryFine said:
The customer on this job lives alone, and is handicapped. He basically lives in front of his computer. His power usage is that of a shed.

It almost seems my questions are being ignored, and I started this thread. :? Please go over my last few posts to put together the facts.

I don't mind the sizing questions and answers, but I would like my questions addressed, too, like whether the disco/ATS nipple requires bonding.
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The nipple needs no extra bonding. As far as sizing 702.4(B) says use art. 220 or another approved method. 702.4(B)(2) says you have to be able to supply the full load or use load shedding. So if there is no load to shed then I'd say you're good to go.

I can't remember when the nonsense about ATSs came into the code but it is pure garbage. There is no good reason for the requirement and it was another case of big money buying a code requirement.
 
LarryFine said:
Which tells us what in relation to my questions?
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That the answers to your questions may be different depending on what code is being cited. A fair number of posters maybe citing the 2014 or the 2017 NEC.

I may have missed it but I don't see any of your questions do not have an answer of some kind. What other questions did you have?
 
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