In my workplace, I have taken on the responsibility of designing industrial control panels. Currently, I am examining an older panel running on 120VAC. In reviewing past designs, I observed that the Engineer used a dual breaker for the incoming 120VAC power, routing both the hot and neutral through each half of the breaker. Per electrical code guidelines, the neutral does not require protection. This raises the question of why the mains hot and neutral were routed through a UL489 20A dual breaker. Upon inspection of the schematics, it appears they may have been anticipating the use of two hot legs in a 208V 3 phase system. However, this setup would result in the remaining branch circuits being inadequately protected, as they are all single breakers on the hot side only.
It's been a while since I last reviewed that section, but to the best of my recollection, it is allowed. However, what is not permissible is a fused connection where the neutral wire can be disconnected without the live wire also being disconnected. This issue arose in a corner-grounded delta system where a load was connected to a fused disconnect. In order to comply with regulations, we had to replace the fuse in the neutral phase with a non-fusible "blank." I was relieved when this system was replaced. Although I'm unsure of the benefits, there must have been a reason for its use. It's possible they had an abundance of 2-pole breakers and needed more 1-pole units.
In Europe, circuit breakers consist of 2 poles for total isolation of the circuit. For a three-phase power supply in a plant with a neutral, the main switch is commonly 4 poles. The neutral provided by the company typically carries a voltage close to zero, but there is a risk of higher voltage due to supply failures. To ensure safety, switches should be unipolar unless a separate 0V is created by using a transformer with one side of the secondary connected to ground instead of the supply's neutral.
Typically, 2-pole breakers are found on machinery imported from overseas, where neither side of the single-phase transformer secondary is grounded. It is important to ensure all non-grounded conductors are properly protected in these instances to prevent electrical hazards.
Joseph_e2 mentioned that while reviewing a certain section, he remembered that a certain type of connection is permissible. However, he emphasized that a fused connection where the grounded conductor could open without the hot also opening is not permissible. He shared an experience with a corner-grounded delta system where a load was on a fused disconnect, and they had to replace the fuse in the grounded phase with a "blank" that didn't have a fusible link to comply with regulations. He expressed relief when the system was eventually replaced. The corner ground installation discussed is not only interesting but also potentially hazardous. While working for an electrical contractor in the Midwest, the author encountered many irrigation pump controllers in systems like center pivot or other irrigation setups. According to the author's boss, the configuration typically involved one phase having a wire straight from the lug to a ground lug, a deviation from standard practices. The author was warned not to tamper with the configuration to avoid encountering a voltage of 277V. The unusual setup was reportedly a cost-saving measure by the utility company to reduce the use of miles of neutral wire. In conclusion, the author highlighted the peculiarities of the corner-grounded installation and the potential dangers posed by unconventional electrical configurations.
When considering purchasing machines, it's worth noting that some OEMs offer both 120 and 220 volt options, allowing for potential conversion. In terms of cost, investing in 2 pole breakers may not be significantly more expensive than 1 pole breakers, and avoiding the need to manage separate inventory could potentially offset any additional expense. Additionally, utilizing a single standard CAD template can streamline the engineering process and save time. A similar cost-saving approach can be seen with ice cube relays, where the efficiency of using 4 pole relays and sockets may outweigh the slight savings of 2 pole options, especially for OEMs dealing with high quantities.
It sounds like you've taken on an interesting project. Considering the peculiar setup, it may be that the original engineer was attempting to accomplish something outside of typical standards, like preparing for the 208V three-phase system you mentioned. However, you've made a great point about the safety concern of possibly leaving the other branch circuits inadequately protected. In these situations, it can often be helpful to have a conversation with the original engineer, if possible. Also, revisiting the current codes and guidelines wouldn’t hurt to ensure the setup is safe and compliant. Ultimately, safety and code-compliance are paramount when dealing with power systems.
It's quite fascinating that you've encountered this in your workspace. The use of the dual breaker might be due to a safety redundancy or a preparatory step in case of a future upgrade to a 208V system - as you've speculated. This approach, however, overlooks the fact that if transitioned to a 208V system, it would indeed leave the other branch circuits unprotected. And this would obviously be a violation of both safety and regulatory standards. Maybe the engineer hadn't fully thought it through or lacked all the necessary information. Regardless, it's essential that the necessary corrections be made to guarantee safety and code compliance. It could involve consulting with a more experienced electrical engineer or even bringing in an inspector, depending on what your company's standard practices are.
I agree with your observation - for a single-phase 120VAC system, running neutrals through a breaker is not recommended nor needed according to NEC guidelines. This practice is typically reserved for multi-wire branch circuits or a 240VAC system where both lines are hot. The original design can be modified to include all necessary protection, but I would recommend a complete review to understand how this panel interacts with your entire infrastructure. It may also be worth getting in touch with the original engineer or consulting a professional to help assess and implement changes without causing disruptions.
In my experience, this sounds more like a design flaw rather than an intentional setup for a 208V 3 phase system. Engaging neutral in a breaker isn't typical and it could also create a safety hazard. Instead, neutral should be routed to a bus bar or neutral termination block. However, it might be worth looking into the specific operational requirements of the equipment in case there's a reason outside our knowledge for this unusual configuration. Always best to double-check such details during any equipment design revision!
✅ Work Order Management
✅ Asset Tracking
✅ Preventive Maintenance
✅ Inspection Report
We have received your information. We will share Schedule Demo details on your Mail Id.
Answer: - The dual breaker was likely used to anticipate the future use of two hot legs in a 208V 3 phase system, as indicated in the schematics.
Answer: - No, according to electrical code guidelines, the neutral does not require protection, so routing only the hot through the dual breaker would be sufficient.
Answer: - Routing both through a dual breaker may result in inadequately protected branch circuits, as the remaining circuits are typically on single breakers connected to the hot side only.
Join hundreds of satisfied customers who have transformed their maintenance processes.
Sign up today and start optimizing your workflow.