Is it a violation to...

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packerdon1

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install a small transformer connected to the t-leads of a 3 phase motor using the existing fusing and overload protection. this is something one of our bosses wants to do to power a small vibrator. I guess i am asking can we power anything from the t-leads other than the motor. I am unsure and I don't want to install this device in this manner, If we can what are the additional things to consider?
 
packerdon1 said:
install a small transformer connected to the t-leads of a 3 phase motor using the existing fusing and overload protection. this is something one of our bosses wants to do to power a small vibrator. I guess i am asking can we power anything from the t-leads other than the motor. I am unsure and I don't want to install this device in this manner, If we can what are the additional things to consider?[/QUOTE
Did you say that the transformer in question also has fuses on the primary such (2) KTKR 600v fuses and (1) secondary FNM 250v fuse for example?
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In addition to the question templd points out, I would be concerned about would motor oveload protectyion if it is not internal.
 
packerdon1 said:
install a small transformer connected to the t-leads of a 3 phase motor using the existing fusing and overload protection. this is something one of our bosses wants to do to power a small vibrator. I guess i am asking can we power anything from the t-leads other than the motor. I am unsure and I don't want to install this device in this manner, If we can what are the additional things to consider?
Click to expand...

I got lost at the vibrator part:)
 
No there isn't fusing on the primary just a fuse on the secondary. Shouldn't there be a disconnect as well as fusing on the primary? what about MOPC this motor is a 1HP 3phase motor. I cannot see how I can reliably detect a motor overcurrent with the motor and the transformer both pulling current from the same source, in this case it will be the O/L heaters. I think the way to do this is to install a dedicated 110vac circuit from a load center switched on/off via a relay signaled from a PLC output. This is the standard installation for this type of appliance. I just don't think this is worth cutting corners and if I can find it to be a code violation I have a case to prevent the man from damaging things.
 
packerdon1 said:
this is my main concern as well as the whole workmanship thing. I just don't do this.
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What I would be looking for is a fused disconnect or breaker feeding the motor starter. The CPT would be feed between the disconnect/breaker and the starter. As such you would have a disconnect for the CPT.
Assuming that the power is 480v (you did not specify so I'm only guessing) you would have (2) properly sized KTKR (600v) fuses on the primary size of the transformer. Should the transformer fail those fused would take the transformer off line. You then would have a single secondary FNM (250v) fuse "assuming that the vibrator is 120v (again, you did not specify). The connection to the transformer that is not fused would be the "grounded conductor."
Again, this is what I would consider a common configuration. But, you left so many of the details out of your description please understand that my explanation is not to be assumed to be what your installation is.
 
Ok Details.

Ok Details.

Here goes,
480V 3 phase MCC feeding a 7A breaker serving as a service disconnect in a MCC bucket, this feeds a motor starter with an overload module attached set for 1.7A (this is the FLA of the motor it protects) also in the MCC bucket. From the Overload module I have a conduit run of around 100' containing the T-Leads feeding the 1hp motor, this setup is existing and running.
The modification is to add a 120vac vibrator to a hopper near the motor which there is not an existing power source, so he wants to install an enclosure near the motor to house the stepdown transformer, this transformer (480v-120v) will be fed off of the existing wiring at the motor (100' from the motor starter and inserted into the existing circuit after the overload module not ahead of the motor starter). I am asking is this circuit design violating NEC by placing the transformer(unfused primary) in the circuit between the overload module and the motor. If so, why? If not, why not?

Thanks
 
What I want...

What I want...

to do is install into the existing low voltage conduit run a dedicated 120vac and neutral from the PLC to power the vibrator, make the required programming edits and terminate this to the 120vac vibrator. This is the standard way I've handled this type of install my entire career and I am in concerned that anyone would not want to do it this way (safe and straight forward install) opposed to the nonstandard convoluted scheme this guy has come up with to save a few bucks. I just want to be able to overrule him with a NEC violation, or feel good that his is indeed safe.
Not to mention the comprimised motor protection due to the fact theat the vibrator will now draw current through the overload module as well.
 
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packerdon1 said:
Here goes,
480V 3 phase MCC feeding a 7A breaker serving as a service disconnect in a MCC bucket, this feeds a motor starter with an overload module attached set for 1.7A (this is the FLA of the motor it protects) also in the MCC bucket. From the Overload module I have a conduit run of around 100' containing the T-Leads feeding the 1hp motor, this setup is existing and running.
The modification is to add a 120vac vibrator to a hopper near the motor which there is not an existing power source, so he wants to install an enclosure near the motor to house the stepdown transformer, this transformer (480v-120v) will be fed off of the existing wiring at the motor (100' from the motor starter and inserted into the existing circuit after the overload module not ahead of the motor starter). I am asking is this circuit design violating NEC by placing the transformer(unfused primary) in the circuit between the overload module and the motor. If so, why? If not, why not?

Thanks
Click to expand...

Why would you not want to fuse the primary of the transformer? IK believe that I explained why you should in one of my previous posts.
Then, the remote motor control with a properly sized OLR coordinated to protect the motor, you are now adding an additional load at the motor, the transformer to power the vibrator. Wouldn't one want to consider the implications of the added load on the OLR?
The worse that could happen is that the OLR would nuisance trip due to the motor load and the load added for the vibrator. To adjust the OLR for the additional load would compromise the motor overload protection.
If you left the OLR as is other than the risk of it nuisance tripping I doubt if there would be a code violation there. But not to include pri. fuses with secondary OCP for the transformer most likely would be which I believe would be covered by NEC art 450.
 
@Tmpldl,"To adjust the OLR for the additional load would compromise the motor overload protection."

This is exactly my concern. The modification wiring is not my idea, I want to install a dedicated 120vac circuit and forget all the goofyness with the transformer fused or not. I so want to find his silly scheme to be a violation so I don't have to fight the battle with him over it.

Thanks for the input.
 
packerdon1 said:
@Tmpldl,"To adjust the OLR for the additional load would compromise the motor overload protection."

This is exactly my concern. The modification wiring is not my idea, I want to install a dedicated 120vac circuit and forget all the goofyness with the transformer fused or not. I so want to find his silly scheme to be a violation so I don't have to fight the battle with him over it.

Thanks for the input.
Click to expand...

Spot on.
To stya within code you can't change the OLR setting to compensate for the extra load otherwise you would compromise motor protection. Providing pri. and sec. protection for the transformer is necessary regardless.
As such providing a separate 120vac supply would be best but you must also consider the length of run and the related voltage drop to assure that voltage drop won'cause you grief after doing all of the work.
If voltage drop is an issue, running a separate 480v supply with a step down transformer at the load may be something that you still must consider. As such, keep an open mind regarding the options that you may have to take into consideration.
 
May or may not be NEC compliant but I would rather see this "accessory" connected ahead of the overload protection at the very least to ensure proper overload protection. The only thing that should be connected load side of overload protection is power factor capacitors - and if this is done overload protection needs adjusted to new current levels as the capacitors will lower net current.

Would be better yet to derive from its own branch circuit in most cases and control via an aux contact on the original motor controller. If items are associated with each other you may have a situation where you can have a control panel and not just a single motor controller - you still want the protected motor to be the only load on the overload device.
 
kwired said:
May or may not be NEC compliant but I would rather see this "accessory" connected ahead of the overload protection at the very least to ensure proper overload protection. The only thing that should be connected load side of overload protection is power factor capacitors - and if this is done overload protection needs adjusted to new current levels as the capacitors will lower net current.

Would be better yet to derive from its own branch circuit in most cases and control via an aux contact on the original motor controller. If items are associated with each other you may have a situation where you can have a control panel and not just a single motor controller - you still want the protected motor to be the only load on the overload device.
Click to expand...

I agree. That would be the ideal way to do it.
 
thanks

thanks

voltage drop is not a concern, I agree the fusing is a non issue as well. My thought the whole time was this is crazy to do, keeping in mind the folks who "designed" this circuit are not electricians or electrical engineers - their only motivation is to cut cost of pulling wire and possibly installing conduit. Mind you these folks are fresh out of college and not well versed in common practices of electricians and/or electrical engineers. None of these people in charge have read any UBC's as far as I can tell, it's almost like having the kindergarten children run the school. I guess this is my burden to bear, each wonderful day. I will put their project to death and design it anew.
 
packerdon1 said:
voltage drop is not a concern, I agree the fusing is a non issue as well. My thought the whole time was this is crazy to do, keeping in mind the folks who "designed" this circuit are not electricians or electrical engineers - their only motivation is to cut cost of pulling wire and possibly installing conduit. Mind you these folks are fresh out of college and not well versed in common practices of electricians and/or electrical engineers. None of these people in charge have read any UBC's as far as I can tell, it's almost like having the kindergarten children run the school. I guess this is my burden to bear, each wonderful day. I will put their project to death and design it anew.
Click to expand...

Remeber that you are the expert and would not be doing your customer a favor by cutting corners. You customer I sure would not hesitate to come back and blame you for a failure should you try to cut corners in an attempt to do your customer a favor.
 
I don't have a problem with it as long as both the motor and xfmr are adequately protected. That may or may not be possible depending on your exact situation. It seems unlikely.
 
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