Generator Breaker

[iceworm]

That breaker on the $500-1000 hardware store genset is not a QO breaker or a Siemens Q series breaker, or any other common thermal magnetic breaker found in a panelboard. It is likely a thermal only type of breaker from most of what I have seen, ....

I did not know that. I have not ever paid attention to the CBs found is package, residential grade generation. Be that as it may, all molded case CBs that I have seen have an inherent instantaneous trip - i've never seen a 'thermal-only'. If you are telling me that hardware store gensets have special CBs, I'll believe you - surprised, but okay.

... it is protecting the genset for the most part and needs to react to heating similar to how a motor overload protector reacts to heating caused by motor current. The impedance of this genset is high enough the short circuit current will not be high enough to get into the instantaneous trip ranges of typical thermal magnetic breakers and they trip on thermal overload anyway. They may or may not select a breaker that has a trip curve that well protects the genset, but I'm guessing most just choose something cheap and it is good enough to get by with. ..

I've had occasion to read through UL 1004-4 and UL 2200. Still, I'm not qualified to comment on small, cheapest possible, hardware store grade, package gen, cost effective design.

Considering what I think I know, for first part (cb protects the gen), I don't know that is true.

The second part, sure - good guess

... I do have a 8000 watt unit that I do use for work when there is no power on site. I even use it for welding somtimes, but the breaker on this unit does trip if I weld at too high of setting/too long of duration. I can run same welder via same cordset that is rigged to fit the generator on a 30 amp QO breaker in my shop (from utility supply) and usually weld at higher setting/ longer duration then I can when running on this generator. But that don't mean all similar sized units will handle it same way either.

Your 8KW has a 240V, 30A, 4W receptacle, protected by ta 30A CB? And has two duplex, 120V receptacles, each protected by a 20A CB? The welder is plugged into the 1ph, 240V, 30A 4W receptacle, protected by a 30A cb, and the CB trips if you pull hard on it? (guessing this cause that is what i had on a Miller Bobcat 225A, with an 8KW aux gen.) If so, sounds good to me. An 8KW is good for 32A +. The 30A cb is for the receptacle, not the gen. Just guesses.

ice

 

[templdl]

I don't think I missed your point. You appear to be stuck on the first CB protecting the gen from all damage. if the discussion is about small residential grade, I don't see any evidence that is necessarily true.

As for "gotten lucky" - hummmm .... don't what to say. Maybe, "Verifying generator data against the selected CB TCC data is called 'making design decisions', not 'getting lucky'.

I still don't know where you are going with this. Perhaps, you could read post 13 and narrow the scope a bit.


Good choice. I think that is called, 'making design decisions'.

ice

I never stayed that the subject breaker would provide generator protection as that isn't going to happen. I understood that to OP was intedingto use the breasker's as a branch circuit protective device as you would size a breaker to protect a the wire for a branch circuit installed panerlboard. Or did I overlook something.
I wasn't aware that generator ptotect was the issu. If there is an attempt to overload the genset the field oftern collapses because it is incaspablt of generating the current. I have normally recommended that the oil pressure. Voltage, etc be monitored and should the genset
Oil pressure drop, the voltage drop etc there would be a contact closure to activate a shunt trip installed in the breaker and trip the breaker.
I believe that I previously stated that in order to tripcurrentmon UL489 breaker you would have to generate 300% if the breaker's rated current for 50 sec for breakers up to 30a, 80sec for breakers up to 50a, 140sec for breakers up to 100a. The mag trp is usually 10x the breaker's rating usually +-20% with the smaller residential breaker that may be less.
The question still remains is if the genset even has the capability of tripping the breaker by sustain 3x its rated current for a long enough time to trip the breaker thermally of if it has that capability to generate fault current that is 10x the breaker's testing.

 

[kwired]

I did not know that. I have not ever paid attention to the CBs found is package, residential grade generation. Be that as it may, all molded case CBs that I have seen have an inherent instantaneous trip - i've never seen a 'thermal-only'. If you are telling me that hardware store gensets have special CBs, I'll believe you - surprised, but okay.


I've had occasion to read through UL 1004-4 and UL 2200. Still, I'm not qualified to comment on small, cheapest possible, hardware store grade, package gen, cost effective design.

Considering what I think I know, for first part (cb protects the gen), I don't know that is true.

The second part, sure - good guess



Your 8KW has a 240V, 30A, 4W receptacle, protected by ta 30A CB? And has two duplex, 120V receptacles, each protected by a 20A CB? The welder is plugged into the 1ph, 240V, 30A 4W receptacle, protected by a 30A cb, and the CB trips if you pull hard on it? (guessing this cause that is what i had on a Miller Bobcat 225A, with an 8KW aux gen.) If so, sounds good to me. An 8KW is good for 32A +. The 30A cb is for the receptacle, not the gen. Just guesses.

ice

Your description of my 8kW generator is possibily more accurate then what I may describe it as - but is not a Miller - just a B&S special I got a a Home Depot. The 30 amp breaker (which is not a typical molded case circuit breaker but looks like a general purpose rocker switch from the operator side of the panel it is mounted on) kills power to all the outlets, and whether or not is designed to protect the generator is a good question, but is in series ahead of the breakers for the 20 amp 120 volt receptacles, so it ultimately is monitoring the entire genset output. Those 20 amp 120 volt receptacle breakers are just a small round mounted in a 1/2 inch hole "pop out" when tripped type of device. My guess is they are thermal only devices and have no instantaneous trip mechanism. Generator impedance is likely high enough it wouldn't put out enough current to trip on IT. I have used it as backup generator at home, it will start my 3 ton heat pump compressor, but you must have nearly no other load connected or it draws voltage down enough it will not start it - but doesn't trip breaker either during this starting attempt because it can't put out enough current to get into IT ranges - at least that is my observation. Heat pump only draws about 6 amps when on low stage in heating mode, and runs fine once started but it still takes a good surge of power to start it.

 

[iwire]

That breaker on the $500-1000 hardware store genset is not a QO breaker or a Siemens Q series breaker, or any other common thermal magnetic breaker found in a panelboard. It is likely a thermal only type of breaker from most of what I have seen, and that is likley all it needs to be on most of those small kVA gensets,

I did not know that.

Neither did I and it is not what I see on small to medium size units.


kwired, can you link to any specs backing that up?

What I see are standard breakers.

 

[kwired]

Neither did I and it is not what I see on small to medium size units.


kwired, can you link to any specs backing that up?

What I see are standard breakers.

When you say standard breakers do you mean something like Square D QO, Siemens Q, GE THQ... series units?

I do typically see those in standby sets intended to be permanently installed, but not in your low kVA portable units, and even in some 10-12 kVA portables.

What I am talking about is not limited to, but sometimes may look like this

 

[iceworm]

temp - We are not on the same page. I don't particular disagree with anything you have said - I just don't approach generator system design anywhere close to my translation of what you do. Here are some examples:

I never stayed that the subject breaker would provide generator protection as that isn't going to happen. ....

Okay. My mistake. I heard a lot of refering to gen protection in your posts.

... I understood that to OP was intedingto use the breasker's as a branch circuit protective device as you would size a breaker to protect a the wire for a branch circuit installed panerlboard. ...

Yes that was my understanding as well. However, you were the first to bring up gen protection by CB (post 8)

.... Or did I overlook something. ...

I think a few things. You have left the field so broad that statements that apply at one end, don't apply to the other end.

I wasn't aware that generator ptotect was the issu. If there is an attempt to overload the genset the field oftern collapses because it is incaspablt of generating the current. ...

NEC 450.12 says generator protection is an issue. And no I would not agree that for residential grade, hardware store types - field collapse is not the load limiting parameter. I would guess the driver horsepower is the issue. WOT and load increases, engine slows down - that's driver horsepower, not field collapse.

... I have normally recommended that the oil pressure. Voltage, etc be monitored and should the genset
Oil pressure drop, the voltage drop etc there would be a contact closure to activate a shunt trip installed in the breaker and trip the breaker. ...

Yes, I've seen your previous posts (other threads) where you have advocated this. I still don't agree.

• Residential grade (untill one gets into the 12KW+ range) don't have an oil pump (Yes, I'm sure you can find an exception)
• The ones that do have an oil pump shut the engine down on Low Oil Pressure - no shunt trip CB
• Under voltage is not a gen protection issue issue. If there are voltage sensitive loads - protect them. Generally one does not see UV trips utill the gen is > 100KW. Even then this is not particularly gen protection - rather system shutdown, because there is something broke. Consider, Voltage is -20%, current is not in overload, no Loss-of-Field - yeah, something broke, time to shut down the system cause the connected equipment is going have trouble. But the gen itself - it will be fine. What ever broke didn't burn up the gen.
• Over current trip, under frequency trip - those I would consider. Maybe 86T the driver, maybe not. So, for maybe $3K - $5K I could fit a GE Multilin, CTs, PTs to a $1000 hardware store gen. Whoops can't even do that. We have at least one inspector that would burst into flames just walking by - becuse we busted the NRTL

... I believe that I previously stated that in order to tripcurrentmon UL489 breaker you would have to generate 300% if the breaker's rated current for 50 sec for breakers up to 30a, 80sec for breakers up to 50a, 140sec for breakers up to 100a. The mag trp is usually 10x the breaker's rating usually +-20% with the smaller residential breaker that may be less. ....

Okay. How about looking at the specific CB TCC instead of UL489 minimums?

... The question still remains is if the genset even has the capability of tripping the breaker by sustain 3x its rated current for a long enough time to trip the breaker thermally of if it has that capability to generate fault current that is 10x the breaker's testing.

Not a question to me. This is all part of generator system design. If it matters (likely not if one is buying package, residential grade, hardware store grades), get the generator data, get the specific CB TCC - Evaluate. Coordination, Protection? Just as much as one wishes to pay for. With enough money, I can coordinate/protect anything. Yep - truth

None of this is meant to imply you are not knowledgeable. Rather - we have significantly different views on gen system design. And you have not limited the scope (see post 13 again) As I said earlier, design decisions that fit one - don't necessarily fit the other end.

ice

 

[templdl]

temp - We are not on the same page. I don't particular disagree with anything you have said - I just don't approach generator system design anywhere close to my translation of what you do. Here are some examples:


Okay. My mistake. I heard a lot of refering to gen protection in your posts.


Yes that was my understanding as well. However, you were the first to bring up gen protection by CB (post 8)


I think a few things. You have left the field so broad that statements that apply at one end, don't apply to the other end.


NEC 450.12 says generator protection is an issue. And no I would not agree that for residential grade, hardware store types - field collapse is not the load limiting parameter. I would guess the driver horsepower is the issue. WOT and load increases, engine slows down - that's driver horsepower, not field collapse.


Yes, I've seen your previous posts (other threads) where you have advocated this. I still don't agree.

• Residential grade (untill one gets into the 12KW+ range) don't have an oil pump (Yes, I'm sure you can find an exception)
• The ones that do have an oil pump shut the engine down on Low Oil Pressure - no shunt trip CB
• Under voltage is not a gen protection issue issue. If there are voltage sensitive loads - protect them. Generally one does not see UV trips utill the gen is > 100KW. Even then this is not particularly gen protection - rather system shutdown, because there is something broke. Consider, Voltage is -20%, current is not in overload, no Loss-of-Field - yeah, something broke, time to shut down the system cause the connected equipment is going have trouble. But the gen itself - it will be fine. What ever broke didn't burn up the gen.
• Over current trip, under frequency trip - those I would consider. Maybe 86T the driver, maybe not. So, for maybe $3K - $5K I could fit a GE Multilin, CTs, PTs to a $1000 hardware store gen. Whoops can't even do that. We have at least one inspector that would burst into flames just walking by - becuse we busted the NRTL

Okay. How about looking at the specific CB TCC instead of UL489 minimums?


Not a question to me. This is all part of generator system design. If it matters (likely not if one is buying package, residential grade, hardware store grades), get the generator data, get the specific CB TCC - Evaluate. Coordination, Protection? Just as much as one wishes to pay for. With enough money, I can coordinate/protect anything. Yep - truth

None of this is meant to imply you are not knowledgeable. Rather - we have significantly different views on gen system design. And you have not limited the scope (see post 13 again) As I said earlier, design decisions that fit one - don't necessarily fit the other end.

ice

I see your point.
The breasker you may be referring to is probably a reverse UR component listed device. It probably has a thermal element more in line with the overload capability of the genset as determined by the genset ma nm ufacturer. and may not have an instantaneous element. In doing so this is about the only way tty he genset protection can be provided.
When it comes to a branch circuit protective deve it can't recall if tyher NEC would allow this genset breaker to provide the required branch circuit protection. The weird this about it is wehern you provide tty he OCD as required by the NEC it end up to be basically a disconnect switch as the breaker supplied we with the genset is more closely match to the power generating capability of the genset.

 

[Tony S]

I’ve only fitted a few small gen-sets (7KVA) but used breakers based on I_r.

As has been said X_d will prevent I_i reaching the point where MCB’s operate.

 

[iceworm]

... The weird this about it is wehern you provide tty he OCD as required by the NEC it end up to be basically a disconnect switch as the breaker supplied we with the genset is more closely match to the power generating capability of the genset.

I agree.
For small generation: in the majority - yes

ice