Mounting fuses directly on reactors?

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LMAO

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Texas
We are using passive harmonic filters which are combination of 2 reactors (line and trap) and capacitor bank (trap) in UL508A VFD enclosure. Line reactor is in series with source and VFD; trap reactor and caps are in parallel (please see below).

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So A1 B1 C1 is the supply, A2 B2 C2 feed the VFD (T1 T2 T3) and AT BT CT are connected to trap circuit via conductors that are smaller than supply (about 40%). My question is: instead of running wires from AT BT CT to fuse mounting blocks, can I just mount the fuses directly on AT BT CT which are just bus bars? Can I just ask the manufacturer whether mounting the fuses on reactor bus bars violate their UL listing?

Thank you
 
Jraef

Jraef

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Electrical Engineer
No. Fuse holders have a mechanical strength (withstand) rating based on the potential magnetic forces that can be in play during the time it takes a fuse to clear. Although you might make an argument that the reactor lugs are possibly strong enough to withstand those forces, whatever you rig together on the other side to keep the fuses apart will not have been tested or approved for that.

100.3, "suitable for the intended use".
 
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petersonra

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Location
Northern illinois
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engineer
Look carefully in ul508a. You will find a requirement that fuses be installed in UL listed fuse blocks.

Having said that, I have had a couple of chats with UL about this kind of thing. My understanding is that they will change your procedure to allow you to mount fuses directly to bus bars if you ask them to do so and pay the required fee. What I gather they do is make you use some switch board standards and the arrangement is only good for 10kA SCCR.
 
Besoeker

Besoeker

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Location
UK
I wouldn't do it. Apart from anything else, if the reactors run at their rating or close to it, they will hot which will affect the fuse rating.
 
Besoeker

Besoeker

Senior Member
Location
UK
Phil Corso said:
Besoeker.

Mal-operation of any one of the fuses could cause havoc! In fact for protection of the "Trap" I would have recommended a breaker!

Phil
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I would never engineer a system where a single failed fuse in such a system would allow it to be continued to be powered.
 
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