If your proposing inserting this circuit in series with the existing equipment ground, it could interfere with ground fault current , if you have one. Which would also slow the circuit breaker reaction time and increase equipment damage. Especially if the diodes fail. The resistor will defeat the ground wire purpose. Interfering with the most important conductor in an electrical circuit is never a good idea.
Next Tech: Ground Loop/Lift
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It has no bearing at all on the circuit breaker reaction time because circuit breakers do not react to ground faults. They can't because they're not connected in any way and can't even see the ground leg.
A circuit breaker reacts to current load per unit time. Large spikes trip the breaker immediately, persistent overload conditions will trip it eventually. Whether that current went to power, shorted to neutral, or shorted to ground has no bearing on how the breaker reacts. Breakers interrupt current flow exclusive of the ground condition.
If the diodes fail they fail they to a closed state - which maintains the ground connection. The resistor is in parallel and is not a gate. It's presence does nothing in a ground fault condition (fails open.) It's only effective when a differential remains below 500 millivolts and both diodes are fully operational.
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I would only consider a HumX type device on a GFCI circuit. I do carry short GFCI equipped extension cords with me (mostly for outdoor gigs but also for bad premise wiring).
Let's assume a failure mode where the line wire came loose inside a DJ mixer and touched the case. If the case is properly grounded, the breaker should trip after so many milliseconds (unless it is an FPE or Zinsco). However, even on the better brands there is a fairly high degree of variability in trip time. This is why we have to worry about the diode failure. Diodes fail to open circuits in over-current situations and this would be an over-current situation. They fail to short circuits in over-voltage situations (aka punch through) which is common in motor and dimmer circuits where there are inductive spikes. If the breaker doesn't trip fast enough you could open the diode and be left with the mixer case at line potential.
Let's instead assume scenarios that are based on modern realities. You may be fond of your pal's presentation but, that information was meant to be all-encompassing, and you're relying too heavily on outdated and obsolete system conditions. What you propose for this tragedy makes perfect sense if:
- our DJ mixer was built in Italy 50 years ago,
- we're "that guy" who stuffs foil in fuse holders,
- we have a 10" table saw in our DJ rig
I understand your pre-occupation with If, if, if..... but, ALL of your concerns can be tested. The current required to COMPLETELY burn open the diodes can be measured. It can be measured with the poorest performing of all common branch breakers in series. (Your worst case scenario.)
A danger is not made manifest merely by our ability to suppose a myriad of system conditions required to support it.
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You're downgrading the design parameters to reach your conclusion, and that's dishonest.
Failure of the HumX diodes is defined merely as the loss of their rectifying quality, which may occur at ground faults drawing over 6A. But, what you are citing is a catastrophic material failure of the solid core conductors which is going to require a persistent over-current condition on the ground leg exceeding well over 20A in the circuit proposed.
We know when the diodes have failed because the HumX no longer breaks ground loops.
We know when the material has catastrophically failed because the HumX smells like toasted baekelite.
The problem with this argument is that you're placing the "fire" ahead of it's cause. There's no reasonable way to burn through a pair of properly rated diodes on the ground leg without ALSO tripping the breaker. There may be other applications where diodes fail as you suggest, but this application is the one being considered.
This device is also not operating on the neutral, it does nothing to slow or stop a surge. Spikes pass directly through to the branch breaker.
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It is simple enough to test. Wire up a heavy cord with a diode between line and ground. Plug it in and see if the breaker trips before the diode blows. The peak instantaneous forward current of a diode is much greater than the rated operating current. However, it derates very quickly with the number of cycles. After 10 cycles it will be derated by ~40%. The peak current will depend on how fast the PN junction resistance rises with temperature. If it rises quickly, it will limit the maximum fault current and delay the breaker trip time (which as you know is a function of the peak current).
LOL. Don't forget the high speed camera so if they both open we can see if the chicken came before the egg.
I'll setup a test that will let me measure the true conditions, hazards where a single diode is not by itself a dead short.
First, I've got to find a 50 year old European DJ mixer.
I was actually talking with Bill Whitlock this afternoon (the guy that wrote that paper) and I mentioned our discussion here. We came up with a simple way to measure the current pulse and the exact time the circuit opens up using a digital storage oscilloscope. We thought it would be a fun experiment once we can stop social distancing. He lives only 15 minutes away and it has been many months since we've grabbed a meal. I am pretty confident I have some spare IN4004s but these are only rated to 1A. Bigger ones may be tougher to find locally.
Sorry you are very wrong. I’ve installed diodes and SCRs so large they’re water cooled. Many have failed open, totally blown apart. You apparently do not understand the purpose of a equipment ground. I’ve been installing electrical equipment since 1977. Please explain how a breaker will trip during a ground fault without a equipment grounding conductor...notice the words “ground fault”. Not a short between the grounded conductor (neutral) and ungrounded (hot) side. there is more emphasis on grounding and bonding then any other connections. That is why proper sizing of the equipment grounding conductor is so important. It has to be able to handle the expect ground fault current to facilitate the breaker opening. Higher impedance slows the breakers reaction time. The longer the let thru current the more the equipment damage. I’ve seen plenty of destroyed equipment because of improper grounding and incorrect breaker settings because the engineers were worried about nuisance tripping. It is the most important conductor. Cut the ground pin on your cable, connect the black lead to the metal casing of your equipment and plug it in. The breaker will not trip because there is no return path...now the equipment casing is energized and a shock hazard.
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It would certainly give you an answer to your concerns. But, at least test using something that's not absurdly under-rated. No one would be surprised to find a single 1A diode toasted on dead short to a 15A circuit. Won't be helpful if you design for failure.
Use two 10A10-T (10A 1000V ) wired in opposing parallel. That's going have a surge rating in the 400A range and an operating temp of 300F
I don't know what's actually inside a HumX - there's no reason for it not to have 10A10 or better, but there's no disclosure as to how they arrived at their 6A rating and whether that owes to their selection of rectifier, attempts at UL listing, or the device category as a whole (aka: consumer tap and pass through devices with plastic housings.)
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I do this all the time. That's why I DJ in a custom tailored 100 Cal suit.
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I’ve worked in the older 40 cal, not fun. Some have cooling devices now. Under today’s NFPA70E rules it should be a rare event to work on anything energized with the exception of utilities. There were very few electrical safety rules when I started. I mostly just drink beer now
I'm not in the trade but I love watching arc-flash videos. The 100 Cal suits don't even make sense. The blast alone is going to kill you via blunt force trauma. At that point, you might as well let the arc cremate you as well.
I toured the USS Ling in Hackensack, NJ before she was vandalized - a diesel/electric WWII submarine. The entire lower part of the sub was lead/acid batteries.
There was a an approximate 10 ft3 room that was fully insulated - rubber walls, floor and ceiling - with huge knife switches in the center, surrounded by a protective cage. The knife switches were actuated by wood arms that extended to levers outside of the cage. As more speed was required, the operator would engage more battery banks. According to the gauges, Flank Speed was 440 Volts Direct Current @ some ungodly amperage. When engaging/disengaging the knife switches, it must have looked like a science fiction movie!
There was a an approximate 10 ft3 room that was fully insulated - rubber walls, floor and ceiling - with huge knife switches in the center, surrounded by a protective cage. The knife switches were actuated by wood arms that extended to levers outside of the cage. As more speed was required, the operator would engage more battery banks. According to the gauges, Flank Speed was 440 Volts Direct Current @ some ungodly amperage. When engaging/disengaging the knife switches, it must have looked like a science fiction movie!
Back in the 79-81 timeframe, I worked at a brass mill (Anaconda) during the summers off from college. One job I had was to drive the ancient (probably 70 years old at the time) ceiling crane from its upper cab. It had long control handles connected to large (30" diameter) "rheostats" in a metal cage below me and every time you moved the levers, the thing blasted sparks. The cage contained the sparks, but it was quite unnerving.
Nobody's underestimating the importance of grounding and neither are we lacking any of the entry level information you're providing. I'm simply rejecting your personal supposition in place of actual testing of a given circuit application.
A fault to ground is only ONE possible condition resolved by breaker interruption, and frankly most of your concerns are better served by GFCI or RCD which also monitors imbalances in the load. There are a myriad of other even more dangerous overload conditions that do not involve the ground lug.
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Why is there a puddle of water by the DJ booth? I said "Do Not Touch the Equipment!!"
Why are you using a wooden stick to move the controls? I said "Do Not Touch the Equipment!!"
Sometimes it takes a while, but they'll learn.
I have a few. I used to teach the NFPA70E (electrical safety) program before I retired. Would often start out the class with them. I also have pics of the boneheads who tried stealing copper from energized equipment. Not pretty...
Sounds like fun, only modern DJ mixers and controllers are typically low voltage DC devices.
If you really intend to do this pulse test I can send you a couple of the actual modules to test.
The ability of the module to pass a continuous current consistent with the integrity of the original ground leg is easier. It only need be added to a simple circuit in front of a socket where bulbs of various ratings from 7w to 3kw energized.