Wrong Siemens bolt on panel screws?

Got a 400A P3 and 600A P4 several months ago. Getting close to finishing the installation. They had different breaker to bus screws then I am used to. I wonder if that's a mess up or a supply chain substitution? Think I should ask / complain? I don't like having two different types of bus screws in the same building.
 

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Note the thread pitch is different. I don't know if the bus fingers are pre-threaded or intended to have threads formed by the screw, if the former then we have a big problem I would say. I'll take a closer look at the threads and see if they look mangled.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
My guess is that the finer pitch one would be used on a bus. Does the length of that shorter screw look like it's enough for the breaker and bus?
 

infinity

Moderator
Staff member
Location
New Jersey
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Journeyman Electrician
I think that both of those type of screws are self tapping so it shouldn't matter what they used as long as they're not too long.
 

rambojoe

Wireman
Location
phoenix az
Occupation
Wireman
Your supply house may have a grip of damaged gear sitting around that you can go through... Does it suck? Yes, but thats why we have the "one guy" behind the counter who helps. The "other" guy will not let you in the back even if he doesnt know what a 277v photocell is..
" That is against the rules, sir"
Go rambo.
 

GoldDigger

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Placerville, CA, USA
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I would say that if they are self-tapping (which I do not see conclusively from your photo) the critical issue is that once one type is used for a particular hole you cannot substitute the other time when re-installing something. That makes it really suck to have both present in one installation.

The bottom one looks like the threads are tapered, but I do not see the grove in the side usually seen in self-tapping screws. Sheet metal screws do not have the groove, but that metal is not thick enough to require a clearance grove to allow the tapping chips to be cleared.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Got a 400A P3 and 600A P4 several months ago. Getting close to finishing the installation. They had different breaker to bus screws then I am used to. I wonder if that's a mess up or a supply chain substitution? Think I should ask / complain? I don't like having two different types of bus screws in the same building.
I'd ask. I don't know if you can get anyone at Siemens, but maybe the supply house knows what's going on. I agree, two different threads in the same building for PB's is just asking for trouble.
 
The longer screws are used elsewhere in the panelboards, but the correct bus screws have always been unique and seem of much better quality. I've installed lots of Siemens panel boards in the last 10 years so I'm very familiar with them. I'm going to put in a RFI on this.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The longer screws are used elsewhere in the panelboards, but the correct bus screws have always been unique and seem of much better quality. I've installed lots of Siemens panel boards in the last 10 years so I'm very familiar with them. I'm going to put in a RFI on this.
This panel had the same screws in the bus holding the breakers in as it did the trim cover. If you look at the holes in the bus they are not tapped. These screws are self tapping.


Breaker Screws.jpg
 

Besoeker3

Senior Member
Location
UK
Occupation
Retired Electrical Engineer
First number is the size, second is the thread pitch in threads per inch. A #10 is a nominal 3/16 of an inch in diameter.
Would be about 5 mm here. I am quite conversant with inches and metres. Gauge numbers like 10-32 i'd have to use a converter like Google.
 
This panel had the same screws in the bus holding the breakers in as it did the trim cover. If you look at the holes in the bus they are not tapped. These screws are self tapping.


View attachment 2562343
Yeah exactly. The "wrong" bus screws are the same as the ones that holds the dead front on.

One way to go about it is call my supply house and just say I need a bag of BL bus screws and see what they send or if they ask further questions 🧐
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
That doesn't mean a lot for me. A thread pitch for me would something like 3 mm or 5 mm for example.
10-32 is VERY close to M5-0.80. The 32 is 32 threads/inch for a pitch of 1/32" or 0.7938mm. A 10-32 screw will screw into a deeply tapped hole over 10mm.

Now for more than you wanted to know, the "English" number system derivation is not known to me, but the size "N" can be converted to inches by 13*N+0.060. Thus a #10 screw is 0.190". The M5 is 0.197".

Many think that a #10 is 3/16"; close, but not exact. What I've been told by 2 different fastener salesmen many years ago is that the product tolerances are such that a modern (we're talking 1970s here, so better yet today) threading machines can make a thread that will meet both the 3/16"(0.1875") and the #10 (0.190") dimension standards, so one screw is sold for both. I'm not sure ...
 
10-32 is VERY close to M5-0.80. The 32 is 32 threads/inch for a pitch of 1/32" or 0.7938mm. A 10-32 screw will screw into a deeply tapped hole over 10mm.

Now for more than you wanted to know, the "English" number system derivation is not known to me, but the size "N" can be converted to inches by 13*N+0.060. Thus a #10 screw is 0.190". The M5 is 0.197".

Many think that a #10 is 3/16"; close, but not exact. What I've been told by 2 different fastener salesmen many years ago is that the product tolerances are such that a modern (we're talking 1970s here, so better yet today) threading machines can make a thread that will meet both the 3/16"(0.1875") and the #10 (0.190") dimension standards, so one screw is sold for both. I'm not sure ...
Unless you are talking some very very specialized precision threads, most bolts or screws if you measure across the threaded portion it's easily 15 to 20 thou under nominal. Even the grip portion is quite a bit undersized (unless of course you're talking about a stripper or shoulder bolt).
 
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