Fused neutral, industrial control panel
Fused neutral, industrial control panel
(OP)
Looking for insight on the neutral being fused inside a control panel that runs a couple servos, plc, and some other control stuff. It's acctually protected with a thermal magnetic breaker. The panel is 208vac, 3ΓΈ, 20A supply with neutral conductor also being supplied. We have quite a few of these systems. They were deisgned prior to my involvement but I maintain them. A plc, dc power supply, power on lamp, and cooling fan are the loads that this neutral supplies. My concern is over safety. I would never design this into a system. Why do you think someone did this? Is it safe? Should I remove these breakers from these systems?
Any insight greatly appreciated!
Kevin
Any insight greatly appreciated!
Kevin





RE: Fused neutral, industrial control panel
RE: Fused neutral, industrial control panel
What would be the best way to describe why this is a significant hazard?
RE: Fused neutral, industrial control panel
Where were the panels built?
RE: Fused neutral, industrial control panel
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If we learn from our mistakes I'm getting a great education!
RE: Fused neutral, industrial control panel
RE: Fused neutral, industrial control panel
BK
RE: Fused neutral, industrial control panel
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Fused neutral, industrial control panel
RE: Fused neutral, industrial control panel
You're exactly right - we do think it is a subject change, so please start a new thread.
RE: Fused neutral, industrial control panel
However, from dealing with maintenance and plant workers in general, I think you have to assume that the majority of them don't know the intricacies of breaker positioning and will always assume that a breaker at the panel is a way to de-energize the panel. If they have to walk across the room to pull the bus breaker or they can just flip the panel breaker, there are some workers who will always choose to flip the panel breaker no matter how much you've trained them that it doesn't safe the equipment. Just from a human factors viewpoint, I'd say that a single pole neutral breaker living by itself on a piece of equipment is always dangerous. To those who don't know better, there is the impression that it safes the equipment.
Recipe for disaster.
I stumbled on a real interesting discussion you sparkies are having here. I'm learning all kinds of stuff!
RE: Fused neutral, industrial control panel
Part of the process is a required voltage test.
It is never a good idea to rely on the position of the breaker handle to determine if a circuit is energized or not.
The breaker on the neutral is weird,a safety concern, and most likely a code violation, if in the US. But since there are 30 panels built like this, it seems that someone thought they had a good reason for putting it there. I'm not 100% convinced he is looking at a neutral, at this point.
RE: Fused neutral, industrial control panel
Having 3-phases and a neutral come to a panel and then taking control power (likely 120V) from one phase to neutral with a neutral breaker for protection is wrong.
If I have interpreted the description of what you have wrong then please correct me.
RE: Fused neutral, industrial control panel
If I had to guess (and my insatiable curiosity makes me do so), I'd say they did it out of a warped sense of thinking they were protecting the control circuit. I say this because I had a junior engineer once propose this to me out of genuine concern, yet flawed logic. The circumstances will help to explain.
We had a 50A 3 pole breaker (and a neutral landing lug) feeding 208Y120V power to a control panel. He was told to use one phase and neutral from the source for the 120V control power. His logic was, the 50A breaker was way too big to protect the control circuit, but he was always told not to have 2 SCPDs on the same circuit (bear with me for a minute here). So he came up with his idea that if he put a 10A fuse on the neutral side of the control circuit, it is protected and he didn't violate his perception of the "no dual SCPD" rule.
I had to question his "no dual SCPD" rule and found that he had once used two identically rated breakers on a circuit; one in a panelboard outside of the cabinet and another inside the cabinet. He was told (by someone else) it is not a good idea to have two SCPDs in series, because you will never know which one had tripped. He took that to mean NEVER having two protective devices in series, even if one was a branch! So the neutral fuse was his way of "solving" the perceived problem.
RE: Fused neutral, industrial control panel
RE: Fused neutral, industrial control panel
RE: Fused neutral, industrial control panel
RE: Fused neutral, industrial control panel
Any ship that may ever be supplied with shore power must be ungrounded when on shore power to avoid possible serious hull corrosion issues. Some ships ground the system through a knife switch that is supposed to be open when on shore power.Most run ungrounded rather than take a chance that the switch will be left closed on shore.
Bill
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"Why not the best?"
Jimmy Carter
RE: Fused neutral, industrial control panel
RE: Fused neutral, industrial control panel
Bill
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"Why not the best?"
Jimmy Carter