Type 1 SPD wired directly to main lugs

[gamp945]

Hello all,

I'd like to discuss installing a type 1 SPD directly to main lugs or main breaker rather than to a dedicated double-pole circuit breaker.

A recent post touched on this point, but the discussion went off the rails. I've been meaning to post about this issue for a while and the discussion in the aforementioned thread prompted me to create this thread.

Note that according to Schneider Electric's installation manual for the HEPD80 that I am installing, wiring directly to the bus via the main lugs or main breaker is an approved installation method. I've attached a photo of an illustration / photo from the manual to this post.

I am not a pro or electrical expert! I think many of the pros/experts on here have concerns about installing an SPD this way for reasons that I don't completely understand. Feel free to share them here.

The reason I'd like to consider wiring the SPD directly to the main lugs is because for my installation, I am installing in a sub-panel in a detached workshop. I can safely de-energize the main lugs in the sub-panel by switching the breaker off in the main panel, removing the concern about permanently installing an SPD on live lugs that cannot be easily de-energized in the event that the SPD needs to be replaced.

I think that wiring the SPD directly to the main lugs has three advantages for my installation. First, I am short on spaces in the sub-panel and wiring directly to the main lugs solves that problem. Second, wiring to the main lugs will protect everything in the panel including the mini-split I am in the process of installing. Third, I believe (but correct me if I'm wrong) that wiring the SPD directly to the main lugs will result in a slightly higher level of protection compared to installing to a breaker on the bus due to locating the SPD slightly further away from the bus breakers.

My question for the experts here is about how to attach the SPD's leads to the main lugs. The installation manual (photo below, link above) doesn't make it crystal clear to me, but I believe it is instructing to use UL-listed ring terminals (example link) to attach to the main lug bolts, underneath the locking lug nuts. Does that sound right?

 

[Gokart]

That is correct. Just make sure you buy the right size lugs (wire and hole size) for the application.

And dont forget to use the specified crimper.

 

[gamp945]

Thanks, Gokart. I am using a Siemens P1224L1125CU for my sub-panel. The manual states that the main lug to bus connection is a 1/4-20 nut, and the HEPD80 uses 14 AWG wire leads. I think that means that Sta-Kon 14RB-14 ring terminals will fit the bill.

I have a generic ratcheting crimper, similar to this Klein version.

 

[alfredeneuman]

The previous thread ended with "Isn't your life is worth more than a call to a licensed experienced electrician?" and you should take that advice.

 

[mike93lx]

You are installing a panel and already are tight on spaces?

Put in a bigger panel. I would not put the wires under the lugs for the feeder

 

[mm08822]

Thanks, Gokart. I am using a Siemens P1224L1125CU for my sub-panel. The manual states that the main lug to bus connection is a 1/4-20 nut, and the HEPD80 uses 14 AWG wire leads. I think that means that Sta-Kon 14RB-14 ring terminals will fit the bill.

I have a generic ratcheting crimper, similar to this Klein version.

I was dissapointed in Schneider's instructions regarding tieing onto the buss connection. They make no mention of torque requirements, use of star washers, etc. They spent more effort detailing how to take the locknut off the SPD.

If I were to choose this method of connection, I would be using a torque wrench to re-install nuts/bolts. Is there enough bolt length available for another star washer and sta-kon?

You will need a sta-kon with a 1/4" clearance hole & #14 wire. They are readily available but probably in 50/100 count.

 

[BrandonV]

The only real issue in the other thread was the bad double tapping and the OP somehow trying to justify it was okay.

 

[Sumboodie]

The previous thread ended with "Isn't your life is worth more than a call to a licensed experienced electrician?" and you should take that advice.

Not like that's the end all be all.

I've fixed plenty of goof ups from experienced plumbers and electricians.

 

[alfredeneuman]

I've fixed plenty of goof ups from experienced plumbers and electricians.

Have you ever removed a tap from energized main lugs without any prior experience?

 

[gamp945]

Have you ever removed a tap from energized main lugs without any prior experience?

Just to clarify, nobody in this thread is suggesting to work on energized main lugs. The discussion here is about installing and/or removing an SPD from de-energized main lugs, following code and manufacturer's approved installation methods.

 

[gamp945]

Does anyone have any thoughts regarding my point #3 in the OP? Does wiring a Type 1 SPD to the main lugs impart any benefit compared to wiring to a bus breaker in terms of surge suppression? Maybe not, but then why are Type 1 SPDs manufactured at all? The impression that I've come away with when reading up on SPDs is that wiring the SPD before the bus (ideally at the meter) is a superior method compared to wiring the SPD to a bus breaker.

 

[alfredeneuman]

Just to clarify, nobody in this thread is suggesting to work on energized main lugs. The discussion here is about installing and/or removing an SPD from de-energized main lugs, following code and manufacturer's approved installation methods

From Post #76 (of the thread gone off the rails)
"Ill tape that wire inplace before cut so i dont need to be touching\holding it while it is cut from live lug."

 

[Max]

Just to clarify, nobody in this thread is suggesting to work on energized main lugs. The discussion here is about installing and/or removing an SPD from de-energized main lugs, following code and manufacturer's approved installation methods.

And as you noted earlier, it's a subpanel so no issues with shutting the power off to the panel.

I personally am not a fan of directly wiring to the main panel lugs as at least some SPDs will use MOVs, and MOVs can and will fail shorted. A good designer will put a fuse in series to prevent issues, and I would hope that you have to do so to get listed. But I'm not sure, so having an upstream breaker is a good thing to me.

https://www.littelfuse.com/~/media/electronics_technical/application_notes/varistors/littelfuse_the_abcs_of_movs_application_note.pdf

 

[mike93lx]

Does anyone have any thoughts regarding my point #3 in the OP? Does wiring a Type 1 SPD to the main lugs impart any benefit compared to wiring to a bus breaker in terms of surge suppression? Maybe not, but then why are Type 1 SPDs manufactured at all? The impression that I've come away with when reading up on SPDs is that wiring the SPD before the bus (ideally at the meter) is a superior method compared to elwiring the SPD to a bus breaker.

Having it as close to the feeder can only serve to help protect equipment if the surge comes in through the feeder.

I am not an EE, so for me it's a matter of do I want to have something tied into a feeder that I can't shut off or do I want to be able to control the devices connected to my panel? That answer is easy for me. Insurance can deal with the rest

 

[Max]

Does anyone have any thoughts regarding my point #3 in the OP? Does wiring a Type 1 SPD to the main lugs impart any benefit compared to wiring to a bus breaker in terms of surge suppression? Maybe not, but then why are Type 1 SPDs manufactured at all? The impression that I've come away with when reading up on SPDs is that wiring the SPD before the bus (ideally at the meter) is a superior method compared to wiring the SPD to a bus breaker.

In theory the closer electrically the SPD is to the voltage source the better job it can do because of lower wiring inductance. This is because a large transient can have a very fast rise time and therefore is therefore composed of a sum of many high frequencies.

In practice I am not so sure that there is any substantial benefit, if any at all.

 

[alfredeneuman]

And as you noted earlier, it's a subpanel so no issues with shutting the power off to the panel.

On another BB he said that it wasn't a sub, and he (or the PoCo) would have to pull the meter.

 

[Max]

On another BB he said that it wasn't a sub, and he (or the PoCo) would have to pull the meter.

Ok. Interesting. He does say a sub panel in his first post so I went with that.

 

[PCustoms]

On another BB he said that it wasn't a sub, and he (or the PoCo) would have to pull the meter.

You sure you're not thinking of another user?

is this to code?

see pic

www.garagejournal.com

 

[gamp945]

@alfredeneuman : did you even read the OP? I'm not the guy from the other thread.

 

[alfredeneuman]

@alfredeneuman : did you even read the OP? I'm not the guy from the other thread.

I apologize. Some posters have different screen names of different BBs.
2 instances of exactly the same obscure issues are rare.

 

[Stuff]

The instructions with Schneider's HEPD SPDs do mention using connectors if attaching to a bus: "Install the crimp lugs onto the black wires by using a UL Listed ring connector suitable for 14 AWG copper solid wire. "

Schneider's panels are designed and tested for use with their SPDs. OP has a Siemens panel and Siemens has never shown anything attached to their lugs. Probably not an issue but might be flagged by an inspector as not listed.