Anyone know the background on fused neutrals?

[sfav8r]

I have posted questions about fused neutrals before, but this one is really a request for a history lesson.

I'm just curious WHY they ever fused neutrals. It is my understanding that this became illegal somewhere around 1927, but I am really curious why this was ever considered to be desirable.

Anyone know?

Thanks.

 

[safeguy]

Re: Anyone know the background on fused neutrals?

Originally posted by sfav8r:
I have posted questions about fused neutrals before, but this one is really a request for a history lesson.

I'm just curious WHY they ever fused neutrals. It is my understanding that this became illegal somewhere around 1927, but I am really curious why this was ever considered to be desirable.

Anyone know?

Thanks.

**************** Some History.....***************


NEUTRAL FUSES (from the 1915 NEC)

* Rule 23a specifies that a (fuse) must not be placed in any permanently grounded service.

* Rule 23b specifies that the fuse must be omitted in any permenently grounded wire, except where a two wire-branch circuit is derived from a grounded-neutral three-wire system, in which case the fuse MUST be inserted.
^^^^^^^^^^^^^^^^

 

[friebel]

Re: Anyone know the background on fused neutrals?

Look at 430.36 Fuses -- In Which Conductor

Where fuses are used for motor overload protection, a fuse shall be inserted in each ungrounded conductor and also in the grounded conductor if the supply system is 3-wire, 3-phase ac with one conductor grounded.

 

[kiloamp7]

Re: Anyone know the background on fused neutrals?

Remember that 430.36 is a rather rare occasion.
First, you need a corner-grounded system, - but you also must be using fuses for the running overload protection in a motor branch ckt.
Most frequently, "heaters" in the 3-phase starter serve that function.

 

[lazorko]

Re: Anyone know the background on fused neutrals?

I wasn't around back then, but I've seen enough old wiring to take a guess. In the days before microwave ovens, a 120V, 30A service was adequate for powering the few lights in a house (no multi - wire branch circuits to consider); knob and tube wiring also may have made it difficult to associate one neutral conductor with a corresponding branch feed. Connecting a new device back then meant lifting a floor board and finding a neutral and a "hot" to connect to. Fusing the neutral ensured that a neutral wouldn't be overloaded as wiring was added onto existing wiring.