Can someone help me explain motor service factor to non-Electrician's?

[don_resqcapt19]

You might cite OSHA violation as the reason. OSHA requires insulation or isolation to be used as protection from equipment that operates with surface temperate high enough to cause that burn. However there is no specific rule that requires this, but OSHA has said in this document that they can issue citations for hot surfaces.

 

[growler]

I am being asked to explain why we needed a more expensive motor for a piece of equipment.
I am authorized to make that decision, however, I have to explain my decision to them.

Purchasing only see's replacement costs, they don't see longer life of the motor.

Can you talk directly to the engineers or techs at the company that manufactured the equipment. They may have all kinds of information about problems with this equipment.

One of two things is happening, either other companies are having similar problems with the equipment and are calling the manufacturer, or you just happened to get a "Lemon".

If a lot of problems occur because the motors are not sized correctly the manufacurer will know about, if they are willing to share this information is another thing.

 

[petersonra]

If the mechanical load is the same, and the motors have similar efficiency, then the current drawn should be the same. The fact that the _overloaded_ 1/2 hp machine was drawing more current than the safely loaded 3/4 hp machine suggests that it was operating much less efficiently, or that the load has somehow reduced.

Unfortunately there is no way to tell just what went on.

Sometimes minor motor misalignment can cause enough extra friction that it increases the HP requirements.

Sometimes cheaper motors have a worse PF, so it may have been drawing a lot of current but not as much HP as the current draw might seem to indicate.

 

[hockeyoligist2]

You might cite OSHA violation as the reason. OSHA requires insulation or isolation to be used as protection from equipment that operates with surface temperate high enough to cause that burn. However there is no specific rule that requires this, but OSHA has said in this document that they can issue citations for hot surfaces.

Thanks Don, that sent me in the right direction! I invited the top "bean counter" to meet me at the machines. I brought a printout of the OSHA link you gave me. I asked her to read it, then asked her to put her hand close to the motors without touching them.

She said "Oh my, that one is hot!" Then I politely explained how it would be expensive and almost impossible to place a guard around the motors. She then asked me to order a replacement motor for the one overheating and replace it as soon as possible.

I will be changing the other motor tomorrow!

P.S. Thanks to everyone else for the feedback. Y'all come in handy quite often! I learn a lot from this forum!

 

[readydave8]

Can you talk directly to the engineers or techs at the company that manufactured the equipment. They may have all kinds of information about problems with this equipment.

One of two things is happening, either other companies are having similar problems with the equipment and are calling the manufacturer, or you just happened to get a "Lemon".

If a lot of problems occur because the motors are not sized correctly the manufacurer will know about, if they are willing to share this information is another thing.

Usually seems like manufactorer will say "No one else is having that problem".

But if I have the problem again later on another job and call they say the same thing.

 

[mtfallsmikey]

A piece of #12 solid shunted across heater elements works pretty good for this on those type of applications. On motors that draw more than 50 amps you may need to use larger conductor

Can I get the formula from you to size the larger conductor? I have AHU motors that draw close to 50 when the VFD is maxxed....

 

[kwired]

Can I get the formula from you to size the larger conductor? I have AHU motors that draw close to 50 when the VFD is maxxed....

It is a highly scientific formula but does not require a calculator. If overload should happen to trip use a larger conductor. If fuse or breaker trips use a larger one. If motor burns out use a larger one, see the pattern yet?