I am a sound and lighting engineer hiring out equipment to schools and clubs for small events (speech days, am dram etc.) I have recently picked up a client that is hiring LED and incandescent lights, amplifiers, and the necessary control equipment. The client runs 6 separate teams doing pantomime shows for schools during November and December and each show has two lighting tripods with two LEDs and one 750W incandescent on each. The operator has an amplifier, sound and lighting desks and radio microphones. Some of this equipment is full mains, others have PSU's of various outputs from 9 to 15V.
My worry is that the client is absolutely insistent that the equipment is isolated from the venue's supply using a single 1.5kVa Isolation Transformer (IT) and will not budge from this attitude.
I know very little about the workings of an IT but have gleaned that the principle use of an isolation transformer is purely to allow the connection of test equipment to a device under test. I also see that if there are multiple devices plugged into the isolation transformer, then those devices are no longer floating with respect to mains earth. Every part of them will either be at earth potential or some other potential with respect to mains earth. That means that user is at risk of an electric shock - perhaps just from touching the case of another item of gear.
I have also found that the IT does not supply a ground link between the input and output Earth pin, therefore making an RCD inoperative and putting the electrical equipment’s casings and any conductive equipment attached to the circuit at risk of being raised to mains potential without anyone being aware should a fault occur within one or more items.
My feeling is that this is an incorrect use of an IT and the client is putting her teams at risk of a lethal shock should any item go to a fault condition. As I am the hiring Company, I am responsible for the safety of the users and I cannot avoid liability, even though it is the client’s insistence to use an IT.
Please can someone explain whether I have understood the reason for using an IT and that I really should insist on replacing them with a rapid action RCD.
Thanks
Nigel Pye
My worry is that the client is absolutely insistent that the equipment is isolated from the venue's supply using a single 1.5kVa Isolation Transformer (IT) and will not budge from this attitude.
I know very little about the workings of an IT but have gleaned that the principle use of an isolation transformer is purely to allow the connection of test equipment to a device under test. I also see that if there are multiple devices plugged into the isolation transformer, then those devices are no longer floating with respect to mains earth. Every part of them will either be at earth potential or some other potential with respect to mains earth. That means that user is at risk of an electric shock - perhaps just from touching the case of another item of gear.
I have also found that the IT does not supply a ground link between the input and output Earth pin, therefore making an RCD inoperative and putting the electrical equipment’s casings and any conductive equipment attached to the circuit at risk of being raised to mains potential without anyone being aware should a fault occur within one or more items.
My feeling is that this is an incorrect use of an IT and the client is putting her teams at risk of a lethal shock should any item go to a fault condition. As I am the hiring Company, I am responsible for the safety of the users and I cannot avoid liability, even though it is the client’s insistence to use an IT.
Please can someone explain whether I have understood the reason for using an IT and that I really should insist on replacing them with a rapid action RCD.
Thanks
Nigel Pye
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