minerleague
Member
- Location
- Mid-Michigan
I had a business man call me recently with a grounding problem. He manufactures ?tanning booths? for commercial use. The interior of the booth is lined with a product called ?solarite? which is a plywood backed sandwich board with a clear powder coating over-top of 0.024? thick aluminum sheeting for a high reflectance.
The other day, an owner of one of his booths received an electrical ?poke? from the aluminum handle while closing the door to the booth. The local electrician measured about 6.75mA current flow from floor to handle. The electrician then bonded the handle to the wall of the booth, and read 0.19mA between. The business man is VERY concerned about his liability with this potential exposure, especially on the other 12,000 units he has already sold across the country. He is asking for my help.
My explanation was that there was clearly a difference in potential between the floor the person was standing on, and the handle that he had grasped. Therefore, my quick response was to install a ground fault circuit breaker on the system, and they couldn?t hold in the GFCI.
Next I had them bond all the different metal parts together to eliminate any difference in potential. Once this was done and measured with a VOM, everything appeared to be fine. So, they applied a meggar tester (2500VDC) to metal parts within the system, and they lost the ground. We can?t figure why. Our guesses are that the 2500VDC melts the powder coat to insulate the made ground connection, or, the aluminum sheeting melts away, or what??? I then suggested we put an aluminum strap (or bar) across the ?solarite? product and lag our grounding screws into that, and it seems to work, even with the meggar tester. I suspect it?s because of the greater surface area ? lowering the current ? therefore holding the ground. But I?m not sure enough to take the liability for this kind of ?fix?. They still can't hold in a GFCI.
Another issue with the manufacturing of this product is that the various electrical devices uses were not ?intentionally bonded? and grounded to a common point. I suggested they put star-washers under all screws mounting metal parts of electrified devices. It also came to light that the aluminum handle was mounted from a steel back-box holding some fluorescent light ballasts which could be the source of some potential static grounding discharge. The ballasts now are mounted with star washers assuring bonded connections to their steel enclosure. But it seems to me that the aluminum handle against steel back-box could be a source for not bonding because of ?dissimilar? metals corrosion.
The business man is very interested in learning the reasons why this is happening and solving this problem. Would you be interested in reviewing this product and making some recommendations on solving this ?grounding? or ?bonding? problem?
The other day, an owner of one of his booths received an electrical ?poke? from the aluminum handle while closing the door to the booth. The local electrician measured about 6.75mA current flow from floor to handle. The electrician then bonded the handle to the wall of the booth, and read 0.19mA between. The business man is VERY concerned about his liability with this potential exposure, especially on the other 12,000 units he has already sold across the country. He is asking for my help.
My explanation was that there was clearly a difference in potential between the floor the person was standing on, and the handle that he had grasped. Therefore, my quick response was to install a ground fault circuit breaker on the system, and they couldn?t hold in the GFCI.
Next I had them bond all the different metal parts together to eliminate any difference in potential. Once this was done and measured with a VOM, everything appeared to be fine. So, they applied a meggar tester (2500VDC) to metal parts within the system, and they lost the ground. We can?t figure why. Our guesses are that the 2500VDC melts the powder coat to insulate the made ground connection, or, the aluminum sheeting melts away, or what??? I then suggested we put an aluminum strap (or bar) across the ?solarite? product and lag our grounding screws into that, and it seems to work, even with the meggar tester. I suspect it?s because of the greater surface area ? lowering the current ? therefore holding the ground. But I?m not sure enough to take the liability for this kind of ?fix?. They still can't hold in a GFCI.
Another issue with the manufacturing of this product is that the various electrical devices uses were not ?intentionally bonded? and grounded to a common point. I suggested they put star-washers under all screws mounting metal parts of electrified devices. It also came to light that the aluminum handle was mounted from a steel back-box holding some fluorescent light ballasts which could be the source of some potential static grounding discharge. The ballasts now are mounted with star washers assuring bonded connections to their steel enclosure. But it seems to me that the aluminum handle against steel back-box could be a source for not bonding because of ?dissimilar? metals corrosion.
The business man is very interested in learning the reasons why this is happening and solving this problem. Would you be interested in reviewing this product and making some recommendations on solving this ?grounding? or ?bonding? problem?
