Whole house generators

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nizak

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Curious as to what the inspection process is for a whole house generator install.

Is it correct to say that the unit has to be able to supply power to the entire connected load?

I realize that load shed modules can be installed to drop out high wattage loads and that in doing so you can reduce the KW rating.

What I am finding is that inspectors are not requesting any type of load data when they are inspecting these installs.

There are quite a few local contractors who are putting in under sized units, charging top dollar, and not getting called out on it.

Does anyone else notice a lack of proper enforcement when it comes to these installs.
 
nizak said:
Curious as to what the inspection process is for a whole house generator install.

Is it correct to say that the unit has to be able to supply power to the entire connected load?
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That is close, but IMHO not quite right.

1. I think it has to be able to supply the calculated load, not the connected load. If it had to supply the connected load it might have to be larger than the POCO service. :)
2. In any case, that condition only applies if an Automatic (ATS) transfer switch is used. And with an ATS the load shed modules must control enough loads to bring the calculated load down to or below the generator rating.
If you use a manual transfer switch there is no minimum size for the generator since it is assumed that the person who is going to throw the switch is capable of manually controlling the active loads first.
 
I have heard a well respected inspector say that he doesn't care if the generator is large enough for the entire load or not. If it isn't and the breaker trips that's not his problem.
 
nizak said:
Curious as to what the inspection process is for a whole house generator install.

Is it correct to say that the unit has to be able to supply power to the entire connected load?

I realize that load shed modules can be installed to drop out high wattage loads and that in doing so you can reduce the KW rating.

What I am finding is that inspectors are not requesting any type of load data when they are inspecting these installs.

There are quite a few local contractors who are putting in under sized units, charging top dollar, and not getting called out on it.

Does anyone else notice a lack of proper enforcement when it comes to these installs.
Click to expand...

Unit doesnt have to be sized for the total connected load, nor the maximum calculated load. Certain appliances like ovens, dryers and spas do not restart on their own upon restoration of power.

We do some "whole house" installs with units that cannot run everything at once in the house simultaneously, but the HO is fully aware of this. Connected loads that could trip the unit out immediately, or automatically, like dual/triple ACs, are load shed. We havent done a whole house install on a home with very high amperage draws like on-demand water heater, spas, EV charging stations, but sufficed to say if a HO with a 400A service wanted to be able to run everything at once, they'd be looking at a 70-120kW generator.

As a Generac dealer that only does the air-cooled models, the biggest gensets we install and service are 22kw, good for about 75A continuous load. When we load test them, it's actually fairly difficult to get electric dryers, ovens, water heaters, ACs, etc all drawing max current at once. Many higher amperage devices are 120V and run from a few seconds to a few minutes at a time, so overloading the generator is hard to do, unless it is grossly undersized.

Load calcs are done tho to balance draw on A and B legs, and to ensure the generator can start and transfer w/o tripping. "Whole house" doesnt mean "run everything at once".
 
702.4(B) uses the terms full load and connected load. It requires either the generator is sized for the full load or the maximum load that is connected with the load management system, so even if you had load shed on say the A/C system it would still need to be large enough to carry the rest of the connected load at one time.

702.4(B)(2) Automatic Transfer Equipment. Where automatic transfer equipment is used, an optional standby system shall comply with (2)(a) or (2)(b).
(a) Full Load. The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment.
(b) Load Management. Where a system is employed that will automatically manage the connected load, the
standby source shall have a capacity sufficient to supply the maximum load that will be connected by the load management system.
Click to expand...
 
infinity said:
702.4(B) uses the terms full load and connected load. It requires either the generator is sized for the full load or the maximum load that is connected with the load management system, so even if you had load shed on say the A/C system it would still need to be large enough to carry the rest of the connected load at one time.
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I think you put a slight twist on the actual words that might get misinterpreted. Manage the connected loads IMO is a bit different from carry the connected loads. Here's more complete text...

702.4 Capacity and Rating.

...

(B) System Capacity. The calculations of load on the
standby source shall be made in accordance with Article
220 or by another approved method.

(1) Manual Transfer Equipment. Where manual transfer
equipment is used, an optional standby system shall have
adequate capacity and rating for the supply of all equipment
intended to be operated at one time. The user of the
optional standby system shall be permitted to select the
load connected to the system.

(2) Automatic Transfer Equipment. Where automatic
transfer equipment is used, an optional standby system
shall comply with (2)(a) or (2)(b).

(a) Full Load. The standby source shall be capable of
supplying the full load that is transferred by the automatic
transfer equipment.

(b) Load Management. Where a system is employed that
will automatically manage the connected load, the standby
source shall have a capacity sufficient to supply the maximum
load that will be connected by the load management system.
Click to expand...
 
nizak said:
What I am finding is that inspectors are not requesting any type of load data when they are inspecting these installs.
Click to expand...
There are quite a few local contractors who are putting in under sized units, charging top dollar, and not getting called out on it. Does anyone else notice a lack of proper enforcement when it comes to these installs.
Click to expand...
Most of the municipalities in my area require you to submit an electric load calc. They're not going to check you on it. You can dummy one up or use the same one on every job if you chose to do so. What they are really trying to do is insure that the unit you're providing is large enough to handle the load in your calc but they never check to see that the unit will actually handle it. If it fails - that's your problem and an issue between you and your customer.

Some municipalities are also requiring a gas load calc. There are several older municipalities in my area with inadequate gas lines in some parts of their towns where the gas co. will not guarantee they have enough gas pressure to operate the unit. I envisioned this when I first started installing gen sets. After the EI inspects your installation he notifies the POCO who comes out to re-seal the electric meter but no one ever notifies the gas co. They have no idea if you're the only one on your street with a gen set or if everyone on the street has one.

As far as inspections go, I get an electrical inspection to insure that I performed the electrical installation correctly, a plumbing inspection to insure that the gas line was installed properly and that the piping holds pressure and in some townships a fire inspection. None of the inspectors want to see an actual demonstration or care whether the unit works or not.
 
infinity said:
I have heard a well respected inspector say that he doesn't care if the generator is large enough for the entire load or not. If it isn't and the breaker trips that's not his problem.
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With all due respect if an inspector said that and someone was willing to testify he said it and a job he passed failed and caused damage or death it will become his problem. As well as the contractor that installed it.
Granted, optional standby systems can fail but if it fails because the contractor half assed it and didn't install it to the NEC He's liable for it and all damages caused by the failure. And a good lawyer will drag the inspector into it too.
 
qcroanoke said:
With all due respect if an inspector said that and someone was willing to testify he said it and a job he passed failed and caused damage or death it will become his problem. As well as the contractor that installed it.
Granted, optional standby systems can fail but if it fails because the contractor half assed it and didn't install it to the NEC He's liable for it and all damages caused by the failure. And a good lawyer will drag the inspector into it too.
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how could it fail in an unsafe way that would cause death or damage? it would just trip if the load was too high.

just like if one hooked up a load that took 200A to a 100A CB. the CB would just trip preventing an unsafe condition.
 
petersonra said:
how could it fail in an unsafe way that would cause death or damage? it would just trip if the load was too high.

just like if one hooked up a load that took 200A to a 100A CB. the CB would just trip preventing an unsafe condition.
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Sump pumps that must run to prevent flooded basements.
Oxygen generators that people depend on for air.
If I paid a contractor to install a code compliant ATS and generator and it failed because he undersized to NEC requirements I would not be too forgiving of him if his install caused damage or death.
 
Smart $ said:
I think you put a slight twist on the actual words that might get misinterpreted. Manage the connected loads IMO is a bit different from carry the connected loads. Here's more complete text...
Click to expand...

I'm saying that with load management if the load management system is for 1/4 of the total load the generator would still need to be large enough to carry the unnamed portion of 3/4 of the total load.
 
qcroanoke said:
Sump pumps that must run to prevent flooded basements.
Oxygen generators that people depend on for air.
If I paid a contractor to install a code compliant ATS and generator and it failed because he undersized to NEC requirements I would not be too forgiving of him if his install caused damage or death.
Click to expand...

Oxygen generators are usually battery backed. In any case there is no death associated with losing power for a short time.

The sump pump might fail to run causing some basement damage but it is unlikely to happen real quick.

I suppose you could come up with a crazy scenario where it might happen but it seems extremely unlikely.

And given the large number of these systems in operation with little in the way of such problems it seems like an overblown idea.
 
infinity said:
I'm saying that with load management if the load management system is for 1/4 of the total load the generator would still need to be large enough to carry the unnamed portion of 3/4 of the total load.
Click to expand...
I know that's what you were trying to say, but it slightly seemed to say with load management in play, the generator had to support the connected load rather than the calculated load of the loads still connected.
 
petersonra said:
I suppose you could come up with a crazy scenario where it might happen but it seems extremely unlikely.
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I didn't say it would happen.
I said if a system failed and it was because it was not installed to the NEC someone is in trouble.
How is a flooded basement a crazy scenario? It happens a lot.
And if I paid you to install a backup power system to prevent it and it failed because it was undersized do you think I'm gonna let that go?
Install it to code. Then you have a defense.
If you don't because you don't agree with what the code says or you know the inspector will pass it, that's not a defense.
JMO
 
If you are not home, it is unlikely you will have enough connected load to cause it to fail. If you are home, you might notice that the power went out (since you have a large load connected) and do some load shedding.:p

Furthermore, just designing it to the current load doesn't mean it won't be too small in the future.
 
petersonra said:
Oxygen generators are usually battery backed. In any case there is no death associated with losing power for a short time.

The sump pump might fail to run causing some basement damage but it is unlikely to happen real quick.

I suppose you could come up with a crazy scenario where it might happen but it seems extremely unlikely.

And given the large number of these systems in operation with little in the way of such problems it seems like an overblown idea.
Click to expand...

Barbqranch said:
If you are not home, it is unlikely you will have enough connected load to cause it to fail. If you are home, you might notice that the power went out (since you have a large load connected) and do some load shedding.:p

Furthermore, just designing it to the current load doesn't mean it won't be too small in the future.
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You beat me to my reply to petersora's post.

I still believe NEC violates it's own "purpose" in 90.1 by making such requirements for an optional standby system. Legally required system I can understand there being rules that the generator be able to handle the transferred load. If you just want a reliable system, that is design issues and the specifications of just how reliable and what failsafe options are included are exactly what you decide how much you want to pay for in the design.


Let me add not only can the generator breaker trip leaving no power, you can also have prime mover failure, run out of fuel, short circuits or ground faults on branch circuits, etc. and still leave you without a desired sump pump or lose power to a freezer full of food, etc. If it is critical enough you probably have an alarm, notification system, or some other back up just in case. If the 200 year flood comes you might just be SOL anyway.
 
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Barbqranch said:
If you are not home, it is unlikely you will have enough connected load to cause it to fail. If you are home, you might notice that the power went out (since you have a large load connected) and do some load shedding.:p
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Absolutely! All Hvac units know not to try and start when only Generator power is available!
No, wait . That's load shedding.
 
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