EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: calzap on August 11, 2024, 04:54:45 pm
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In some cases, the core is part of or constitutes most of the frame. See the first pic. In others, it’s not obvious. See the second and third pics. If core contacts the frame, the transformer is mounted on a metal chassis, and the chassis connects to earth that would connect the core to earth. That should be a safety factor in case a primary conductor contacts the core. If the chassis is not connected to earth ground and the transformer core is connected to the frame, a primary conductor contacting the core could make the equipment dangerous.
Mike
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#2 is a bell transformer with a provided green earthing wire, presumably this a legal transformer and the core is earthed if/as required.
#3 is a split bobbin design, I think that might count as double insulated?
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Consider each transformer on a case-by-case basis. The hi-pot voltages and locations may give you an idea about the level of separation the transformer is designed and manufactured to. If the transformer says it is tested 4000Vac primary-secondary and 2000Vac primary-core and secondary-core, then there is an implied high degree of isolation between the windings and between the windings and the core. Worry about a wire touching the core is probably not necessary. But in general, there is no issue with earthing the bracket/core if you so wish.
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If the chassis is not connected to earth ground and the transformer core is connected to the frame, a primary conductor contacting the core could make the equipment dangerous.
If you consider primary conductor being floating inside device and contacting the core you should also consider primary conductor contacting the chassis?
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If the chassis is not connected to earth ground and the transformer core is connected to the frame, a primary conductor contacting the core could make the equipment dangerous.
If you consider primary conductor being floating inside device and contacting the core you should also consider primary conductor contacting the chassis?
Yes, that would be standard design procedure if the chassis or any metal connected to the chassis is exposed to touching. And common even if the chassis and any metal connected to it is not exposed to touching.
Mike