Why doesn't your breaker trip?

JNCarr

Joe
Corporate Member
There's been several different posts about duct collection systems and among those are references to (generically) "shop vacs" with various peak horsepower ratings.
As an electrical engineer, I have always been baffled and dismayed by the php ratings given by manufacturers. Since most of these units are plugged into 110VAC outlets, here is a table of the required amperage for the various php ratings. Most of us have 15 or 20 Amp service at each outlet, so why don't those with vacs rated above about 2hp trip the breaker? Inquiring minds want to know...
 

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McRabbet

Rob
Corporate Member
The simple answer is that the manufacturers use misleading information to hype their products. Your table is dead on correct, but they commonly use the peak amperage draw with a locked shaft at startup so they can use that number as applied to the create their HP numbers. For example, my "6.5 HP" 16-gallon ShopVac runs comfortably on a 20 amp circuit with other power draws running at the same time and has never tripped the breaker. I'd estimate that it is really about 1.5 to 2 HP. By contrast, the 240 VAC 5 HP Leeson motor on my ClearView Cyclone draws 6-8 amps with no air flowing and is rated at 21.5 Full Load Amps. With several gates open, it might draw 15 amps.
 

Oka

Board of Directors, Vice President
Casey
Staff member
Corporate Member
Most of the info DIY Euip manufacturers state is total fiction.
In general, 746 watts is 1hp. That is in ideal perfect no resistance terms.
To clarify a 750w motor would have 1 hp x power eff. factor which is most times. .80 or .85. So actual output would be .80-85 hp.
The easy way to look at this is use as an estimate 7.5 amps (yeah I know that is higher than actual) draw to 1 hp @120v.
Now if your home has a cheap breaker like homeline brand then, the Performance will be suspect. Remember most breakers are like an automatic choke, meaning it has a heat sensitive bi- metal assembly that expands with heat to trip it. If the wire or tool does not cause enough resistance (heat) the breaker does not trip. If the breaker is crap it does not trip. If the claimed stats are bogus and inflated the breaker will not trip when you expect.
The reality is you have to look at the the diy tool motor tags then run your own Calcs to figure what is really what. Sad , but true.
Cavaet emptor
 

JNCarr

Joe
Corporate Member
Yeah - it was a rhetorical question - Rob has it right. They lock the rotor and pump current into it till the motor burns up! Then back calculate the HP. Not at all meaningful/useful. And Oka, that's input current so no efficiency factor needed.

My point in bringing this up is to expose a metric that means essentially nothing, yet even reputable companies use or reference it. Dust collection relies on two factors - flow and velocity. A "vacuum" does not move dust, the right balance of flow and velocity does. HP ratings (even if they were meaningful) do not convey any sense of flow and velocity.
 

tvrgeek

Scott
Corporate Member
And we no longer seem to have any consumer protection agency. Advertisements can be total BS and there is no one to stop it. We can't even trust UL or CSA any more, as DeWalt sells power tools that pull 16A continuous with loaded currents over 21A on a 16 gauge cord with a 15A plug with an internal 17A bi-metallic breaker. UL and CSA certified.

Missing from the above conversation on breakers is that they are not a yes/no that trip at come magical current. Their only function is to prevent the structure wiring from catching fire if a load fault. Even a continuous current of the rating does not trip them. They have margins built in. No simple number as it depends on current and time. Domestic breakers are usually magnetic, not bi-metallic.

But yes, total made up specs that have the goal of not informing, but suckering you into thinking their 2.1 HP. is better than the other brand 2.0 HP. As if HP had more than a vague relationship to the actual performance of any tool, vacuum or another. Impellor design, housing design, restrictions of the filters and on and on.

All I know for sure is my Fein Turbo II works great. My Craftsman shop-vac circa 70's makes more noise than vacuum, and in recent objective testing, the Festool, Fein , and Makita dust-collection vacs were top of the heap, DeWalt close to the bottom.

PS Many tools state "HP equivalent" which is another way of admitting BS. Mostly on universal motor tools which are not directly comparable to induction motors anyway. Every motor design has slightly different characters. Then the confusion between HP as power consumed vs the motors ability to do work. Enough to confuse real engineers ( briefly of course) , poor public.
 

Oka

Board of Directors, Vice President
Casey
Staff member
Corporate Member
Good point-Yeah I was trying to state too much in a short time frame. I was writing this when I was waiting for my heart stress test at the hospital...... gotta love the "getting older thing"
Yeah - it was a rhetorical question - Rob has it right. They lock the rotor and pump current into it till the motor burns up! Then back calculate the HP. Not at all meaningful/useful. And Oka, that's input current so no efficiency factor needed.

My point in bringing this up is to expose a metric that means essentially nothing, yet even reputable companies use or reference it. Dust collection relies on two factors - flow and velocity. A "vacuum" does not move dust, the right balance of flow and velocity does. HP ratings (even if they were meaningful) do not convey any sense of flow and velocity.
 

bob vaughan

Bob Vaughan
Senior User
The HP ratings of hobbyist type tools has been a standing joke since the 1970s. These days they've just gotten more technically verbose about the deceptions. Amp draw is about the only number one can use to keep things between the fences.
 
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tvrgeek

Scott
Corporate Member
The HP ratings of hobbyist type tools has been a standing joke since the 1970s. These days they've just gotten more technically verbose about the deceptions. Amp draw is about the only number one can use to keep things between the fences.
But that does not account for the total efficiency and the actual power delivered to the work, be it a vacuum or an edge. OK, most universal motors are similar, but not the same. At least with stationary tools, there are only a couple of motor manufacturers and everyone uses the same motors. Unless talking about DVR which have totally different torque curves.
 

bob vaughan

Bob Vaughan
Senior User
But that does not account for the total efficiency and the actual power delivered to the work, be it a vacuum or an edge. OK, most universal motors are similar, but not the same. At least with stationary tools, there are only a couple of motor manufacturers and everyone uses the same motors. Unless talking about DVR which have totally different torque curves.
So what's your point?
 
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JNCarr

Joe
Corporate Member
Shop vacumns are rated in "air horse power," which is a BS term thought up by the manufacturers. FYI, BS used here does NOT stand for band saw.
I don't think so. Air horsepower is a legitimate term - it is the horsepower needed to move a given volume of a gas (in our case air) against a given pressure by a specific fan. So if it were truly marketing hype as suggested, manufacturers would want the LOWEST number to prove how efficient their fan design was. In other words, why would you want to buy a vac that took 6.5hp to move a given amount of air against a given pressure when the other model does it for 2hp?
 

Gotcha6

Dennis
Staff member
Corporate Member
This topic was discussed here several years ago with the same resulting frustration. Reminds me of a notice sent out by one small engine manufacturer several years ago settled a class action lawsuit by offering a rebate to verified customers for selling the same engine with several HP ratings. Someone held their feet to the fire on that one. Doubtful anyone is going to do the same for a $60 shop vac or a $500 dust collector.......
 

tvrgeek

Scott
Corporate Member
So, why do we suppose advertising copy writers have any clue what technical terms mean let alone consumers in a bib-box store. Bigger is always better, right?
 

drw

Donn
Corporate Member
SInce we are on the topic of non-tripping circuit breakers, my son recently bought his first house, which is 42 years old. In the process of installing new ceiling fans we ran across a non-tripping circuit. Because he had several electrical concerns, he called an electrician, who tract down some of the issues which seem to be the result of a former owners DIYs. While he was there the electrician suggested that my son periodically "exercise" the breakers...meaning switching them off and on! He said that breakers collect dust on the contacts and that exercising them burns it off. I'll have to admit that I have never heard of exercising breakers...is this standard practice?
 

JNCarr

Joe
Corporate Member
There are mixed theories on exercising breakers. Aircraft and other machines that use DC current should definitely do it due to potential electromigration/fusion, even though the contacts are theoretically made of the same metal. If AC contacts are closed as in normal operation, there is little chance of dust getting in between in a normal home environment. And electromigration is not a problem. There MAY be some logic in keeping the mechanical parts moving/greased. Any electromechanical system over about 15-20 years needs to be reviewed and or replaced.
 

drw

Donn
Corporate Member
There are mixed theories on exercising breakers. Aircraft and other machines that use DC current should definitely do it due to potential electromigration/fusion, even though the contacts are theoretically made of the same metal. If AC contacts are closed as in normal operation, there is little chance of dust getting in between in a normal home environment. And electromigration is not a problem. There MAY be some logic in keeping the mechanical parts moving/greased. Any electromechanical system over about 15-20 years needs to be reviewed and or replaced.
Thank you, Joe.
 

Gotcha6

Dennis
Staff member
Corporate Member
Many years ago when doing super market remodels we were confronted with a failed 1200 amp switch gear. It turns out the maintenance man had never lubricated it. There was a procedure the manufacturer called for to do this annually which had never been performed. Other than that I've never heard of exercising a breaker. Given the breaker is in an enclosed panel and in the closed position as mentioned above, it seems unnecessary. I do know that some breakers can be purchased as 'switch rated' which means that they are usually turned off frequently rather than using an inline switch.
 

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