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Buzzer and bell transformer

Merry Christmas
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hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
I have buzzer and bell transformer 120VAC to 24VAC. Below is what engineer sent.

0862bbf7705f9808872b014a83a5100e.jpg




I have following questions:

1. Would that require system bonding jumper? I am not sure if NEC 2017 Article 250.30 applies or not.

2. Would that require grounding electrode conductor secondary?

3. Would that require secondary overcurrent protection?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
It would depend on the specific details of "T-1" but normally "No" to all your questions.
 

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
I have buzzer and bell transformer 120VAC to 24VAC. Below is what engineer sent.

0862bbf7705f9808872b014a83a5100e.jpg




I have following questions:

1. Would that require system bonding jumper? I am not sure if NEC 2017 Article 250.30 applies or not.

2. Would that require grounding electrode conductor secondary?

3. Would that require secondary overcurrent protection?
The rules for Power Limited Circuits are very different. Please check Article 725.
 

rc/retired

Senior Member
Location
Bellvue, Colorado
Occupation
Master Electrician/Inspector retired
This is no different than a standard doorbell transformer.120 volts go in, 24 volts come out.
Chances are that the transformer will be installed on a metal box and will be "grounded" by proxy.

Ron
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
This is no different than a standard doorbell transformer.120 volts go in, 24 volts come out.
Chances are that the transformer will be installed on a metal box and will be "grounded" by proxy.

Ron

Yes it used for bell or buzz type application.

Anything in NEC 2017 that says grounding electrode conductor and system bonding jumper not required for these types of transformer?
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
It won’t hurt anything bonding it, usually just a bond jumper wire. You don’t have to use a grounding electrode if that’s your question.

I don’t see where in NEC 2017 it says bonding jumper is required or not required for this type
of transformer? I got it wouldn’t hurt
 

rc/retired

Senior Member
Location
Bellvue, Colorado
Occupation
Master Electrician/Inspector retired
Yes it used for bell or buzz type application.

Anything in NEC 2017 that says grounding electrode conductor and system bonding jumper not required for these types of transformer?
In this application, no special bonding is required.
I, like every other electrician on this site have installed hundreds of these.
As an inspector, I've inspected hundreds.
You are good to go!

Ron
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
Yes and 250.20(A)

Transformer is 100va primary 120V and secondary 24V used for door bell or buzzer application in cash registers or front of door.

So according 250.30(A)(1) exception 3 system bonding jumper is required but then 250.20(A) system bonding jumper is not required?
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
250.20(A) says its not required to be grounded, so its permitted to be an ungrounded system.
250.30(A) applies to grounded systems.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Yes it used for bell or buzz type application.

Anything in NEC 2017 that says grounding electrode conductor and system bonding jumper not required for these types of transformer?
Start with 250.20(A) that tells you the 24 volt system is not required to be a grounded system. If it is not a grounded system, there cannot be a system bonding jumper as that only exists on grounded systems.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
I guess if you really want to over think things technically 250.30(B) would apply to a ungrounded class 2 xformer, but then 251.121 Exception permits a wire type branch circuit equipment ground.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Start with 250.20(A) that tells you the 24 volt system is not required to be a grounded system. If it is not a grounded system, there cannot be a system bonding jumper as that only exists on grounded systems.
But 250.20(A) allows it to be a grounded system, and the schematic posted shows a grounded secondary.

250.30(A)(1) Exception 3 then provides relief on the System Bonding Jumper size in this application. Does anything provide relief for a GEC connection for such an installation?

Cheers, Wayne
 
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