Engineered for commercial power distribution, the Siemens NGB2B125B is a 2-pole, 125A molded case circuit breaker with a fixed thermal-magnetic trip mechanism. This bolt-on breaker mounts into Siemens P1, P2, and P3 panelboards. It is the predecessor to the 3VA51 series, which requires a separate mounting kit. Delivering 100kAIC at 240VAC and 25kAIC at 480Y/277VAC, it handles demanding environments and supports reverse feed applications.
Which Siemens panelboards are compatible with the NGB2B125B?
This breaker is designed for use in Siemens P1, P2, and P3 panelboards. It mounts directly to the bus using a bolt-on connection.
Can the NGB2B125B be used in DC circuits?
Yes, it is rated for DC applications up to 125/250VDC with a maximum interrupting capacity of 14kA.
What wire sizes are accepted by the standard lugs on this breaker?
The factory-installed lugs accept 8 to 1/0 AWG copper wire or 8 to 2/0 AWG aluminum wire.
What does the LI trip function indicate on this breaker?
The LI designation means the breaker provides Long-Time (thermal) and Instantaneous (magnetic) protection. Both trip settings are fixed on this thermal-magnetic model.
What is the difference between the NGB, HGB, and LGB circuit breakers?
These breakers share the same physical footprint within the GB frame family but offer different interrupting ratings. The NGB provides standard interrupting capacity, while the HGB and LGB offer high and extra-high interrupting capacities, respectively.
How does the NGB2B125B connect to the panelboard bus?
This is a bolt-on circuit breaker. It requires a bolted connection directly to the panelboard bus, which provides a secure, vibration-resistant installation compared to plug-in alternatives.
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Reviews
Review summary
Customers rate this product 4.5 out of 5 based on 8 reviews.
Siemens NGB3B015B - 15A 3 Pole Molded Case Circuit Breaker
I recommend this product
Rated 5 out of 5 stars
9/16/26
480v breakers
The breakers work great
BP
Bland P.
Verified Buyer
Reviewing
Siemens NGB3B100 - 100A 3 Pole Molded Case Circuit Breaker
I do not recommend this product
Rated 1 out of 5 stars
7/22/26
NO LUGS!!
I ordered this breaker and it arrived with no lugs. It was advertised as new so we didn't open the box and check until the shutdown we needed it for. When we discovered the lugs were missing we sent an email requesting a set overnighted. We didn't get a response for a couple of days, at which point we had already ordered lugs from their competitor Simply Breakers. They asked for pictures and questioned weather we had ordered the correct breaker asking if we needed lugs on both sides. This is a panel breaker and their is only one configuration that I am aware of which is bolted to bus in panel and wires to the three lugs on the other side. I have never had to order lugs separately for this style of breaker. They asked for pictures of box and what was in it, of course at this point the breaker is already installed and the box is thrown away. I sent a receipt for the overnight lugs from Simply breakers and asked for whatever credit they could provide. I received crickets to date. I have never had a problem with an order in the past from super breakers, but they are to busy to even respond to my request so I will think twice before I order anything from them again. It will be my last option once all others have been exhausted. Use Simply Breakers they have better stock and service.
PF
Paul F.
Verified Buyer
Reviewing
Siemens NGB3B060B - 60A 3 Pole Molded Case Circuit Breaker
I recommend this product
Rated 5 out of 5 stars
6/24/26
Great service, quick shippin
Need I say more.I have used SB. When we need it and need it quickly Always have what I need.
BP
BJ P.
Verified Buyer
Reviewing
Siemens NGB3B020B - 20A 3 Pole Molded Case Circuit Breaker
I recommend this product
Rated 5 out of 5 stars
5/11/26
NGB3B020B
I recently purchased the NGB3B020B and I’m very satisfied with the quality and performance. The breaker feels solid and well-made, and installation was straightforward. It works exactly as expected and provides reliable protection for my electrical setup. Shipping was fast and the product arrived in excellent condition. I would definitely purchase from this seller again.
RS
Radovan S.
Verified Buyer
Reviewing
Siemens NGB3B050B - 50A 3 Pole Molded Case Circuit Breaker