Originally Posted By: jpeck
This post was automatically imported from our archived forum.
The wording changed in 1975, then changed again in 1999 when an exception was incorporated into a positive statement instead of an exception.
Instead of making it easier to read, it complicated it.
Previously, in 1996 and before (back to 1975) it said:
E. Plug Fuses, Fuseholders, and Adapters
240-50. General.
(a) Maximum Voltage. Plug fuses and fuseholders shall not be used in circuits exceeding 125 volts between conductors.
Exception: In circuits supplied by a system having a grounded neutral and having no conductor at over 150 volts to ground.
Which means that you cannot use plug fuses on circuits where there is more than 125 volts between conductors.
Unless it was supplied by your standard grounded neutral system like almost all houses are.
Now, it simply states you cannot use them for circuits over 150 volts between conductors, but you can use them on circuits supplied by a system with a grounded neutral (like the typical house wiring), except that you also have the 125 volt between conductor limitation. You can do (1) or (2), but you can do so as long as (1) and (2) are true. Poor wording.
V. Plug Fuses, Fuseholders, and Adapters
240.50 General.
(A) Maximum Voltage. Plug fuses shall be permitted to be used in the following circuits:
(1) Circuits not exceeding 125 volts between conductors
(2) Circuits supplied by a system having a grounded neutral where the line-to-neutral voltage does not exceed 150 volts
They were trying to incorporate the exception into the statement and it got all screwed up.
I guess what I am saying is it should not be done (for safety reasons, such as you pointed out), but when (if) the wording is corrected, it will be OK again. You are correct in pointing out that one side will still be hot when one fuse if blown and the other is not.
Did that make any sense? If it did, please explain it to me. 
--
Jerry Peck
South Florida
