Tapped Motor Leads

Status
Not open for further replies.
B

buck$98

Member
I was working with some electricians this morning and came across the following circuit. I have never seen this done before and thus would at least categorize it as " Non Customary Practice"; however, I question if it is acceptable by code.

I have a breaker, motor starter & OL relay located in the MCC with Start/Stop controls from a PLC. Located near the motor the T-Leads pass thru a box. Inside the box a 480/120V transformer is tapped into two of the motor leads. The transformer leads are fused appropriately and the 120V side of the transformer is used to power a bell and light.

Any thoughts?
 
Its odd since the transformer will only be powered while the motor is running, but maybe that is desirable in this case.

The only issue I might have with it is that it does add some load. And that load goes through the overloads, but not through the motor, so the overloads will trip at a lower motor current than might otherwise be expected.
 
I don't see a code violation, and in this case I don't think an indicator light or bell will draw enough current to adversly affect the overloads. But what if it was a big enough load that it would require increasing the size or something?
Just out of curiousity... the bell and light are always on while the motor is running or do they have a switch of some kind that indicates end of cycle or low oil or something?
 
DaveTap

The system is on a small gantry crane. The light, a small strobe, and the bell are to indicate that the crane is moving.
 
I worked at a facility that had several large swamp coolers that had 480 volt fan motors. It was common practice to tap off of L1 and the t4 and t7 lead to get 120 volts to run the pump. Never had any problems (or inspections)
 
Also common practice for motorized dampers at a supply or exhaust fan - tap a transformer off of two of the 480 phases at the motor disconnect and use the transformer to drive a 120 volt or 24 volt actuator. In this case, the transformer is typically only 100va and the actuator itself is usually less than 50 so the additional load is less than 1/2 amp. This isn't exactly meaningless if the fan motor is only 2 or 3 HP, but it seems to be common practive and I've never seen it questioned by an inspector.
These are usually class 2 transformers which are an exception from the normal transformer protection requirements in article 450.
 
Status
Not open for further replies.
Top