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Electicians! Question about fuse substitution
I am afflcted with a 70 amp rated Royal Electric Company type XJ-48 fuse. Not to exceed 250 VAC rating. It's old (like about 70 years old). It blew for no known reason (wiring checks out with a megger).
Is there any good reason I can't substitute a Littlefuse Time Delay 70 Amp 250 VAC FLNR series for it? Dimensionally the same.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
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Comments
Is your old fuse the changeable link type?
Years ago you could buy just the links and the ends of the cartridge would unscrew for changing.
Not in use any more as there was some replaced with just copper wire for the link, never a blown fuse then.
I may say, somewhat parenthetically, that this place is an electrician's nightmare... all done to code -- but to the codes in force when various work was done. Interesting...
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
On NON MOTOR circuits fuses (in general) are sized for the wire so for a 70 am circuit #4 wire is normal
On a motor circuit only the old "one time" fuses were sized at up to 300% (3x) the motor running load. Time delay fuses are usually sized at up to 175% (1.75x) the motor load.
Motor circuit fuses have to handle the starting current which is why motor circuits are allowed to be "overfused" but only when the motor has overload protection either inside the motor, a motor starter or a vfd
Feeder wire should be #4 copper or #2 aluminum.
The "three" separate conductors is bothering me a little. 2 hots and a neutral? What are they using for the equipment ground?
Maybe they are using the neutral for an equipment ground as well which would be illegal nowadays. Don't know if that was legal in the old days. You only see that on older stoves and electric dryers
Just like the main service disconnect for the premises.
If I read my trivia history correctly, the 3 wire circuit for dryers, ranges, wall ovens and cooktops started during WW2 to save copper for the war effort.
There were attempts to change this thru several code cycles but only happened about 12-15 years ago.
The main cables are #4 copper, so that should be good. And yes, it is the older style farm wiring -- the neutral is bonded at the outbuilding sub panel, and there are grounding rods (how good they are I haven't a clue...) from that panel.
Thanks all!
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
Point being they are sized to last a very long time but can still blow eventually even if nothing is wrong.
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch