Need help with fuse selection in fusible Safety Switch / Disconnect

[Phillip Mitchell]

I just got a new phase converter (10 hp Phase Perfect) and am starting to approach wiring the unit. It does not come with an on/off switch (for all that $$$….) and I want to install a physical disconnect / safety switch just before the single phase input / line side so I don’t have to use the circuit breaker as an on/off switch and need a bit of help.

I found a great price on a reconditioned / surplus Square D 2 pole 100 amp fusible safety switch - model D223N

I went with this model / size because PP actually recommends a 70 amp breaker for this converter - input is spec’d by PP as 62A @ 240v, fwiw. I currently have 4 ga wire on a 60 amp 240v (single phase) circuit as the existing line circuit for my old RPC. Despite not having the 70 amp breaker currently, I wanted to future proof the size of the safety switch to not have to upgrade later on (going with 100 amp opposed to more common 60 amp.)

The question: the safety switch did not come with fuses installed. There are black metal clips clamped onto to each of the fuse holders. I’m not even convinced I need this switch to be fused, but the switch was available for the right price and hoping to make it work.

Trying to get the proper replacement fuses on order so I can move along with the installation. The inside of the safety switch box says class H, K or R fuses can be used.

The distance between fuse holders is ~6” and looks more like a blade type should fit (?) What size / type of fuses should I use here given the details?

I am going to call my electrician to do the install, but want to have everything on site and ready to go to prevent him from having to make multiple trips, especially if it needs to be ordered. I have done plenty of my own wiring and know basics, but this is slightly outside of my experience and comfort zone to be 100% confident with.

Thanks for any help.

[Bill Dufour]

Too late now but I bet a 70-100 amp breaker and box would be cheaper then the switch and two fuses plus some spares.
Bill D

[Phillip Mitchell]

Well, I’m $80 into the safety switch so far. Fuses will add some to that.

The circuit I’m using is already on a 2 pole 60 amp breaker in the main panel box. I’m confused why I would want/need a 2nd breaker and box?

My only function for the safety switch is to use it as a more conveniently located on/off switch as a quicker and easier disconnect ahead of the converter from receiving incoming power.

[Cameron Wood]

I have some old ones that are the same as this. I believe that K & R types are time delay- used with large motors.

https://www.amazon.com/Bussmann-BP-N...ct_top?ie=UTF8

Jumping with copper bar would be fine as you already have overcurrent protection- then it is just the disconnect.

[Phillip Mitchell]

I have some old ones that are the same as this. I believe that K & R types are time delay- used with large motors.

https://www.amazon.com/Bussmann-BP-N...ct_top?ie=UTF8

Jumping with copper bar would be fine as you already have overcurrent protection- then it is just the disconnect.

Thanks for the reply. Is jumping with copper safe in this application? I was under the assumption it wasn’t, but I am no an electrician.

[Jim Becker]

If you don't need the fusing and only want the safety disconnect, I believe you can use jumpers but they must be jumpers made for the purpose. Your electrician can provide details and help you find them...electricians use them all the time in meter housings for new or upgraded service for testing and/or until the utility approves the install.

[Cameron Wood]

I would probably take some 1/2" copper pipe and pound the ends flat, but talk to your electrician.

(GC, 40+ years, lots of electrical)

[Ron Selzer]

$18 for 2 used fuses
Bussmann Fusetron FRN-R-100 Dual Element Time Delay Fuse 250 V | eBay

[derek labian]

“ just before the single phase input / line side so I don’t have to use the circuit breaker as an on/off switch”

I have a 10hp PP unit and while it doesnt come with a “on off switch” its designed to accept a simple dc switch to control its power. Are you sure you unit isnt the same? 10 bucks on amazon.

[Phillip Mitchell]

Hey Derek, thanks for the reply. I talked to PP about this and asked them as well about their “on/off” switch option (that is a lot more than $10 through them…)

The tech told me that switch option is on for controlling the 3 PH output and that it was not tied to controlling the input side. Then I clarified and said “so if the unit is wired directly and the breaker is on then it is always on/powered?” And he said yes. I want to be able to isolate the converter completely when I’m not in the shop and using it and not have to use the breaker for that which could be at least a couple times a day at minimum.

That’s why I’m going down the road I am. Hopefully I was told the correct information. A DC switch would be a lot less $ than a 100 amp disconnect and what comes with it.

Do you mind posting a photo or 2 of your switch / setup? Thanks

[Cameron Wood]

Should work. Type L (thicker wall) would be good.

IMG_4391.jpeg

[derek labian]

The tech told me that switch option is on for controlling the 3 PH output and that it was not tied to controlling the input side.

Right. I didn't see any need for an input disconnect because the unit is effectively idle when the output is turned off. Once you turn on the output it engages. Its like any other appliance, ready to go. For example a microwave has power and you can see its "ready" but the magnetron is idle until you start it. If I need to turn it off I'll turn it off at the breaker, which is within a couple of feet. See picture below: System Off.

Do you mind posting a photo or 2 of your switch / setup? Thanks

Screenshot 2023-08-14 at 7.31.11 AM.jpgScreenshot 2023-08-14 at 7.31.23 AM.jpg


I think a fused disconnect is great, but I put one on my house rather than on the PP. The PP has a fuse internally, as well, if I remember correctly. Should be easy to find out.

Hope that helps,

Derek.

[Bill Dufour]

I just meant that in my experience, buying used, a small breaker box and breaker is cheaper then a switch box and fuses. For some reason people ask more money for a high amp switch then a breaker of the same amps.
I use square D QO panels and breakers. Still being made today and the 70 year old ones still fit. So there are a lot of cheap old ones out there. They also make a QO plug in surge protector. I added that to both panels in the shop because of VFDs and DRO's. Cost about $30 on the bay.
Bill D

[Rollie Meyers]

I would probably take some 1/2" copper pipe and pound the ends flat, but talk to your electrician.

(GC, 40+ years, lots of electrical)

That idea should be filed in the same place as using a penny behind a plug fuse, using green insulated conductor as a line conductor, or using a match to see how much gas in in the can, there are dummy fuses made by the major fuse manufacturers because there are applications where they are required by code, but under no circumstances should someone make their own handy hack dummy fuses, they will not seat in the fuse clips properly leading to overheating.

[Bill Dufour]

For a big machine like a RPC code requires a disconnect visible from the machine. This can be a cord plugged into an outlet or a breaker/switch that can be seen to be off when standing at the machine.
BilL D