Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
(OP)
Is there an electrical engineering calculation why the code does not allow more than 1.8m or 6 ft of flexible conduit in installations such as taps for lighting fixtures or motor terminations?






RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
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RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
Yes, you understand correctly -- if you run an equipment grounding conductor inside the flex, you are essentially unlimited regarding the length of the flex. Beware that some local authorities might not agree with that statement, though, so I'd recommend checking with them first.
RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
PeeBee
I think your intent is correct but I believe there is a rule of thumb 100 ft limit to the distance of the EGC listed in table 250.122. Beyond that 100 ft there should be some checking to ensure that the fault current will trip the OC device in a reasonable length of time. A reasonable length of time is determined by the engineer.
RE: Why 1.8 meters (6 feet) is the maximum length of flexible conduit?
The EGC needs to comply with 250.4(A)(5) or 250.5(B)(4), which both require the EGC to provide a "permanent, low-impedance circuit" to ensure that fault current is properly carried and/or tripped. That requirement applies to any installation -- even if you're using rigid conduit or thinwall as the EGC. That could well require a larger-sized EGC than those listed in Table 250.122.
NEC does not dictate any 100-ft rule of thumb on that, it applies to all installations.... so be careful with the rules of thumb....