Fusing downstream with very short cable length
Hi, first post newbie here.
I have a question relating to what I am told is a grey area in both 7671 and low voltage assemblies regs. I have a customer with some LV industrial control panels, 100A fused isolator with 25mm main singles from isolator down to motor drive, but off the isolator terminals are also some short 6mm cables that go immediately to 1A fuses (within 3 or 4 inches). I am aware obviously this contradicts the requirement for conductor CSA rating to be > upstream protective device rating, but also on the other hand have been told in the past this is fine to do as long as the under-rated cable is of sufficiently short length, there is no danger of mechanical damage to the cable, and the design load of its downstream circuit is suitably low - I believe all of those to be true in this case. So the opposite of de-rating I guess! Has anyone had a similar quandary in the past, and if so were able to find a definitive answer within the UK regs?
Entire circuit is enclosed within a steel control panel. Drawing attached, as well as layout sketch of the installation, unfortunately I don't have photos of the actual installation sorry.
Thanks in advance
Ed
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Fusing downstream with very short cable length for more information
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Hi, first post newbie here.
I have a question relating to what I am told is a grey area in both 7671 and low voltage assemblies regs. I have a customer with some LV industrial control panels, 100A fused isolator with 25mm main singles from isolator down to motor drive, but off the isolator terminals are also some short 6mm cables that go immediately to 1A fuses (within 3 or 4 inches). I am aware obviously this contradicts the requirement for conductor CSA rating to be > upstream protective device rating, but also on the other hand have been told in the past this is fine to do as long as the under-rated cable is of sufficiently short length, there is no danger of mechanical damage to the cable, and the design load of its downstream circuit is suitably low - I believe all of those to be true in this case. So the opposite of de-rating I guess! Has anyone had a similar quandary in the past, and if so were able to find a definitive answer within the UK regs?
Entire circuit is enclosed within a steel control panel. Drawing attached, as well as layout sketch of the installation, unfortunately I don't have photos of the actual installation sorry.
Thanks in advance
Ed
Fusing downstream with very short cable length for more information
You may reply to this message here.