Control Transformer Grounding in Washdown areas
Control Transformer Grounding in Washdown areas
(OP)
By code in Canada, control transformers must have there secondary side grounded. I have come across a number of installations in the food industry where the secondary side of the control transformer is not grounded. This is only on machinery that has large amount of water used in the process, and the machinery is washed down daily. The manufacturer said this minimizes the chance of an electric shock to the operators.
Is there any validity to the manufacturers arguement for not grounding?
Is there any validity to the manufacturers arguement for not grounding?





RE: Control Transformer Grounding in Washdown areas
The manufacturer’s logic is flawed. Ungrounded-secondary circuits can float above “0” (ground) or “120“ volts that is predictably found in machine-tool control circuits. Transient ground faults on ungrounded circuits may raise voltage to ground well above the nominal RMS value. Primary-to-secondary faults or leakage in the serving control-power transformer may also cause overvoltage conditions. Both conditions will increase the likelihood of control-circuit insulation failure, and likely increase electric-shock hazard.
RE: Control Transformer Grounding in Washdown areas
RE: Control Transformer Grounding in Washdown areas
If the control transformer secondary is not grounded, a fault can impress voltage on metallic parts without tripping a circuit breaker or blowing a fuse. This voltage is hazardous with respect the other end of winding and that part of circuitry since the full secondary voltage is faced.
However, the control transformer secondary grounding should follow industry standards and electrical safety code including Authority Having Jurisdiction.
RE: Control Transformer Grounding in Washdown areas
RE: Control Transformer Grounding in Washdown areas
I hope I am misunderstanding you. Do you mean that you do not ground the transformer so that if you do have a fault, you size the insulation rating to handle the fault and not arc?
If so, this is only acceptable if you have a Impendance Grounding System installed. Otherwise, regardless of the insulation level, you are leaving the fault current to find its own path to ground. Which can be thru personnel.
RE: Control Transformer Grounding in Washdown areas
Visit
http://www.elect-spec-transformer.com/isotrany.htm
http://www.elevatordrives.com/elevsupportapptipdecember2002.htm
http://www.quadtechinc.com/newsletter/035125.pdf
etc. for more info