Edison Base Fuses

[abrace]

All,

240.51 and 240.52 basically states that edison base fuses can only be used as replacements and that we should move to rejection bases.

My question is when fuses are used solely as motor protection. In that case does 240.51 and 240.52 apply and require only rejection base fuses even though a dual-element time delay fuse is being used only as overload protection per 430.32 and there is something else upstream in the circuit providing ground fault and short circuit protection?

 

[ActionDave]

I don't claim to have seen it all, but I have never seen an Edison base fuse on a dedicated motor circuit.

Is this a theoretical code scenario or a real life installation that prompts the query?

 

[abrace]

Actiondave,

Really more theoretical. Cooper/Bussman sells handybox/box covers that take edison base fuses for the purpose of providing motor overload protection. They can have rejection bases installed in them, but it just got me to thinking.

These things are obviously only suitable for small motors, like for small wall mount ventilation fans and the like.

https://www.platt.com/platt-electri...rs/Cooper-Bussmann/SSU/Product.aspx?zpid=9119

 

[kwired]

Actiondave,

Really more theoretical. Cooper/Bussman sells handybox/box covers that take edison base fuses for the purpose of providing motor overload protection. They can have rejection bases installed in them, but it just got me to thinking.

These things are obviously only suitable for small motors, like for small wall mount ventilation fans and the like.

https://www.platt.com/platt-electri...rs/Cooper-Bussmann/SSU/Product.aspx?zpid=9119

That is same application that I have run into in the past where I have had inspectors wanting a rejection base installed.

My problem is if you try to give a specific protection level to a particular motor - say you need a 6 amp fuse - the rejection base that accepts a 6 amp fuse still lets you put in up to a 15 amp fuse plus you already have a 15 amp overcurrent device as the branch circuit device anyway.

Most small single phase motors though already have built in thermal protection so additional fuse protection isn't normally necessary, but I do see the potential confusion if you should decide to provide additional protection.