A smokin' hot motor

[Coppersmith]

Owner is out of town and doesn't want to deal with motor until he comes back. I'm just hoping he's not going to try and blame me for the new motor burning up. (We don't know if it did yet.) I'll take a little blame, but seems to me the engineer for thing should have specified heaters, and the original installer should have known it needed heaters. If the thing was properly overcurrent protected in the first place, I would not have even been there. On the plus side, I now know a lot more about motor protection.

 

[kwired]

Owner is out of town and doesn't want to deal with motor until he comes back. I'm just hoping he's not going to try and blame me for the new motor burning up. (We don't know if it did yet.) I'll take a little blame, but seems to me the engineer for thing should have specified heaters, and the original installer should have known it needed heaters. If the thing was properly overcurrent protected in the first place, I would not have even been there. On the plus side, I now know a lot more about motor protection.

Most general purpose single phase motors already have integral overload protection. This one being designed specifically for pumps (from what I recall) however likely needs additional overload protection.

 

[JFletcher]

You must have outrageous utility bills, I figured 7.5 hp even if only 80% efficiency would only cost me maybe around 70 cents an hour to run.

I get roughly the same as you. Maybe he meant $30 a day and lives in an area where electricity is 20-30c/kw-hr

 

[Jraef]

Most general purpose single phase motors already have integral overload protection. This one being designed specifically for pumps (from what I recall) however likely needs additional overload protection.

To this point, it's also possible that this is not the original motor, and the original one DID have integral thermal protection, so the original circuit design was legit. Then when it went bad (again, probably because someone opened a valve and repeatedly overloaded it), nobody noticed that the replacement motor did NOT have integral thermal protection and needed a different circuit. It's hard to know the complete history of something like this if you were not there from the beginning.

 

[Electric-Light]

Do you guys not have an ammeter?
If it's drawing much more than the name plate, then you stop there.

You'll have an idea if it's dragging if you run it dry briefly and observe or listen how it slows down.

 

[Besoeker]

Do you guys not have an ammeter?

Jraef mentioned measuring the current in post #3 and, of course, it's the obvious thing to do.

 

[drktmplr12]

Too late to measure the current

Any update on this? I'm interested to know the result.

I'll take a little blame, but seems to me the engineer for thing should have specified heaters

You shouldn't take the blame for lack of motor thermal protection, unless you designed the electrical system. Trying a 70 amp breaker to get the thing running wasn't a great idea and you may have to answer for that. The electrical designer should take blame for misrepresenting the work scope (failure to identify code required equipment) and redesign to provide motor thermal protection. Either way, you should absolutely get paid if you have to supply and install a motor controller.

If an EE designed the motor feeder circuit, they should have made sure overload protection was provided, either integral to the motor or external. If they didn't know this they shouldn't be consulting, imo.

 

[Coppersmith]

Too late to measure the current

Any update on this? I'm interested to know the result.



You shouldn't take the blame for lack of motor thermal protection, unless you designed the electrical system. Trying a 70 amp breaker to get the thing running wasn't a great idea and you may have to answer for that. The electrical designer should take blame for misrepresenting the work scope (failure to identify code required equipment) and redesign to provide motor thermal protection. Either way, you should absolutely get paid if you have to supply and install a motor controller.

If an EE designed the motor feeder circuit, they should have made sure overload protection was provided, either integral to the motor or external. If they didn't know this they shouldn't be consulting, imo.

I agree. I'm waiting for the client to call me back to work on it (and kinda hoping he never does.)

 

[kwired]

Trying a 70 amp breaker to get the thing running wasn't a great idea and you may have to answer for that.

My answer to that is Square D's motor calculators recommend an 80 amp breaker for a 7.5 HP single phase motor, and that NEC allows up to 100 amp before it must fail to start on that before you can upsize it even more.

 

[drktmplr12]

My answer to that is Square D's motor calculators recommend an 80 amp breaker for a 7.5 HP single phase motor, and that NEC allows up to 100 amp before it must fail to start on that before you can upsize it even more.

I can see that argument being made, except the calculator (slide card, right?) states that 80A thermal mag is for short circuit protection only and depends on an enclosed starter with overload heaters for thermal protection. Taken without this context, that argument can work. However, it would be cherry picking information.

 

[kwired]

I can see that argument being made, except the calculator (slide card, right?) states that 80A thermal mag is for short circuit protection only and depends on an enclosed starter with overload heaters for thermal protection. Taken without this context, that argument can work. However, it would be cherry picking information.

Yes, slide card calculator is what I was going off of. In general there needs to be separate motor overload protection. I also find it a little surprising the OP's motor started without tripping the 40 amp breaker

 

[harmony]

start current

start current

Be aware that an el. motor will increase current up to 8 times in the start moment. So it is strange that the 40A breaker doesn't trip at once. But i assume the breaker are VERY slow type. You should increase the breaker amp from 40 A to 70 A . That should be sufficient, but be aware that sudden load also will affect the start current.

But you must install a O.L. . This for save the motor if the load, pump or other external issues are working abnormal.

O.L. will be setup after motor sign 31A

 

[kwired]

Be aware that an el. motor will increase current up to 8 times in the start moment. So it is strange that the 40A breaker doesn't trip at once. But i assume the breaker are VERY slow type. You should increase the breaker amp from 40 A to 70 A . That should be sufficient, but be aware that sudden load also will affect the start current.

But you must install a O.L. . This for save the motor if the load, pump or other external issues are working abnormal.

O.L. will be setup after motor sign 31A

Long feeders/branch circuits will limit that starting surge, so can impedance of the source. Then it depends on the instantaneous trip level of the breaker as to whether it will start without tripping, though I am a little surprised it apparently has started on a 40 amp breaker.

 

[meternerd]

Did anyone actually read the current, both peak starting, running and with the valve throttled (if there is one)? They may be satisfied with less flow due to a throttled valve rather than an up-sized supply. Just a thought. Being the cheapskate that I am, that's probably what I'd settle for. But you could have motor problems, so you need to measure the motor current with no load and voltage (at the motor itself) at full load to verify no wiring problems or motor problems. Sounds like you're assuming overload. Might not be. Please don't shoot arrows at me.....

 

[drktmplr12]

Did anyone actually read the current, both peak starting, running and with the valve throttled (if there is one)? They may be satisfied with less flow due to a throttled valve rather than an up-sized supply. Just a thought. Being the cheapskate that I am, that's probably what I'd settle for. But you could have motor problems, so you need to measure the motor current with no load and voltage (at the motor itself) at full load to verify no wiring problems or motor problems. Sounds like you're assuming overload. Might not be. Please don't shoot arrows at me.....

There is not any overload protection although it is required by code. Properly sized bimetallic overloads will protect the motor from exactly what happened. If he wasn't there to shut off the motor it would have caught fire. Throttling the valve will achieve the desired affect, but whats to stop someone from coming back in 2 years and opening the valve again, only to start a fire?

 

[meternerd]

There is not any overload protection although it is required by code. Properly sized bimetallic overloads will protect the motor from exactly what happened. If he wasn't there to shut off the motor it would have caught fire. Throttling the valve will achieve the desired affect, but whats to stop someone from coming back in 2 years and opening the valve again, only to start a fire?

Honesty?:happysad: I didn't read all of the posts, so my suggestion is STUPID....sorry!

 

[ptonsparky]

[/B]

Honesty?:happysad:

You can be honest and still have no idea what you’re doing.

 

[kwired]

You can be honest and still have no idea what you’re doing.

Which is what happens with most non electricians getting involved in electrical work.

It does make anyone qualified for a career in politics though.