# Industrial Ground Fault Detector(s) - Propose suggestion



## 5yearold (Sep 20, 2017)

We are purposefully isolating the secondary of large transformer used for industrial electric heating.

This isolation is allowed by the NEC 250.21

NEC 250.21(B) "Ground Detectors shall be installed"

I have Googled and found Bender Ground Fault Detectors.

Just curious if anyone has alternate suggestions for a competitive quote.

Thank You


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## Helmut (May 7, 2014)

5yearold said:


> We are purposefully isolating the secondary of large transformer used for industrial electric heating.
> 
> This isolation is allowed by the NEC 250.21
> 
> ...


Sure, call at least 3 Electrical Contractors in your area who specialize in Industrial work, explain to them what you want and why, and they can provide you with a quote.


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## Helmut (May 7, 2014)

Or better yet, explain in a little more detail what you are proposing to do, and what the heaters are for. 

You in the trade?


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## frenchelectrican (Mar 15, 2007)

5yearold said:


> We are purposefully isolating the secondary of large transformer used for industrial electric heating.
> 
> This isolation is allowed by the NEC 250.21
> 
> ...


This is a serious stuff and did you get the Electrical Engineer to help you on this ?

There are few different type of ground fault detectors on market but you left out alot of details on this.


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## triden (Jun 13, 2012)

5yearold said:


> We are purposefully isolating the secondary of large transformer used for industrial electric heating.
> 
> This isolation is allowed by the NEC 250.21
> 
> ...


Are you resistive grounding or fully isolated ground? Either way, you'll need an engineer involved. I prefer the iGard line of products for NGR's.


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## Moonshot180 (Apr 1, 2012)

API instruments, LFE corp, GE make ground indicating meters. Fairly simple to install and work on.

Some ground meters operate using a light bulb and a photo cell. As the indicating needle moves past an alarm setpoint needle the light is interrupted and the photocell de-energizes.


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## hardworkingstiff (Jan 22, 2007)

5yearold said:


> We are purposefully isolating the secondary of large transformer used for industrial electric heating.
> 
> This isolation is allowed by the NEC 250.21
> 
> ...


http://www.eaton.com/Eaton/Products...gRelays/GroundFaultMonitoringRelays/index.htm

I will say I think the Bender unit is pretty nice.


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## paulengr (Oct 8, 2017)

5yearold said:


> We are purposefully isolating the secondary of large transformer used for industrial electric heating.
> 
> This isolation is allowed by the NEC 250.21
> 
> ...


Ungrounded systems were popular decades ago. It is still mandatory on U.S. Navy ships. It SEEMS like a good idea...three light bulbs that you check once in a while and the first ground fault us "free". I have years of experience with this. However, here are the major down sides.

1. How often do you check and how fast should you respond to a ground fault? Factory Mutual for instance says to treat it like a fire alarm and you must have continuous 24/7 monitoring like a guard shack, because basically its a safety alarm. It gives you time to orderly shut down the process, not run that way for months.

2. Finding a ground fault on an ungrounded system us a huge pain. You have to go around flipping breakers and switches off until by trial and error you isolate it. There is no fault current to measure.

3. Everything is supposed to be maintained by qualified electricians which can be a problem for some sites. Especially idiot operators and operations managers that want to just keep running because nothing stopped working yet.

4. With an arcing fault (most common), it interacts with your system capacitance and turns into a charge pump that puts out about 600-800% of line voltage and shreds your weakest insulation. What's the weakest? All your motors. Ungrounded plants have about 4 times the failure rate of other types of grounding. But hey I work for a motor shop, so that's good for business for me.

5. In a double ground fault (line to ground to another line) which happens on your second fault, the grounding system impedance typically keeps the current low enough so nothing trips. Then what? Its called burn down. You have dangerous conditions where your grounded panels are energized. You basically have to burn up lots of stuff until it clears itself. IEEE standards talk about a case where over 40 motors were wiped out one by one over the course of a couple hours of one of these. Hence why Factory Mutual among others has such a dim view of these things and specifically says to upgrade to something else asap. You're going the opposite way.

There are by the way many options for grounding but just two that make sense. You use solidly grounded systems (most common in U.S. because that's all residential electricians are allowed to use because of the prevalence and historical nature of the Edison three wire 250/120 system). The third one you haven't found yet is resistance grounding, either high or low. High resistance grounding is where you insert a resistor big enough to drain the system capacitance (item 4 doesn't happen), and you get a current you can use for detecting and tripping on ground fault (item 1-3 and 5 above). On a typical system the fault current is so low you don't damage a #14 wire. You can coordinate tripping like over current although it is done differently. It has been around for years. It is mandatory in underground and coal mines. It is common in large petrochemical plants. iGard is a vendor but the most expensive. Post Glover is another. If you know enough about them you can easily buy the relaying from anyone . You CAN use a pulser version which shorts out part of the resistor on a timer which helps troubleshoot because you will see a pulse (high/low current) on your amp clamps when it works...but tracing ground faults on high resistance grounds about 25-60% of the time end up being the same as doing it with an ungrounded system (shut everything off then turn it back on one at a time until you find it). So its a nice trick but not generally worth the money.

How good does this stuff work? If you have a ground fault on 4160, usually the equipment is destroyed. With high resistance grounding you have to find the burn spot. Not only that but with tripping its less than the current needed to cause a fatal shock in an accidental line-ground incident. An electrician near me about 5 years ago forgot he had an energized disconnect on 4160 and bumped a transformer with his elbow holding a wrench in a ground. Lots if pain and some red marks but he walked away on Friday and didn't report it until Monday. Another one two years ago took a hit from his hands to his feet with a 7200 V system and is working at my wife's place today. I know both these guys personally. I don't want to make this a safety rant about the mistakes that were made, only to point out the inherent safety features of high resistance grounds.

Low resistance is another option. It is LESS destructive than solidly grounded and sometimes used in the higher voltages of medium voltage distribution where high resistance can't be used but other than managing fault current it doesn't really have anything else going for it. And there are various resonant grounding systems that are just bad all over except you can get away with smaller equipment. So as I said. There are really just two practical options.

So before starting on this path talk to your business loss insurance carrier first to avoid a massive and painful premium increase that management and accounting aren't going to be happy about that saves them all the money they are "saving" in down time, never mind huge increases in motor repair budgets. I'll be happy to send you a truck to exchange your motors every week as a routine stop though. That's what we do for our customers that do this.

Just be careful with some of these vendors. They tend to undersize resistors because it makes the quote lower but may be so low it doesn't drain the capacitance making it effectively ungrounded. Engineers unfamiliar with this stuff tend to make the opposite mistake and end up low resistance grounded because they don't know what works. A good resistor size is 1/3 of the system capacitance (expressed as Xc). Usually at 480 15 A is a good number overall...big enough to eliminate Xc buy small enough to fit in most panels and not burn up wiring. At 4160 I usually use 25 A because its kind of a standard in mining. But I have seen vendors like GE and iGard sell 1-4 A systems in huge enclosures that are undersized based in the transformer alone.

Also keep in mind the most common ground faults are in motors as they wear out. You want/need an overload relay that also trips on ground fault. There are some inexpensive ones on the market. One is even sold by a traditionally very overpriced vendor (Allen Bradley).

PM me if you need more info.

Sent from my Galaxy Tab 2 using Tapatalk


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