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Old 12-11-2016, 07:47 PM   #1
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I'm working on a test and I am not sure of some of the definitions.

What is a starter bucket? I am thinking of a starter inside of a MCC.
Do you think that might be the same thing?

What are two advantages of a high resistance grounded system?
What is the disadvantage of a high resistance grounded system?

My question is, what is a high resistance grounded system, and why would you use it?
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Old 12-11-2016, 08:05 PM   #2
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Quote:
Originally Posted by jbfan View Post
I'm working on a test and I am not sure of some of the definitions.

What is a starter bucket? I am thinking of a starter inside of a MCC.
Do you think that might be the same thing?

What are two advantages of a high resistance grounded system?
What is the disadvantage of a high resistance grounded system?

My question is, what is a high resistance grounded system, and why would you use it?
Yep, starter bucket is the starter cab inside mcc.

Here is a good article on high resistance grounding
http://www.eaton.us/ecm/groups/publi...u02701001e.pdf
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Old 12-11-2016, 08:45 PM   #3
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Whats up Keith?
Seems an old hand like you would be done taking tests. I hope all is well.
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Old 12-11-2016, 09:20 PM   #4
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Whats up Keith?
Seems an old hand like you would be done taking tests. I hope all is well.
Long story short. to be considered qualified now, I have to take and pass this test by the end of the year.
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Old 12-11-2016, 09:38 PM   #5
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Only disadvantage I can think of on an HRG system is that I believe the faulted part can assume a voltage well above earth potential which creates a shock hazard until the fault clears. But I've honestly never seen or heard of it happening, probably because the trip times on these systems are often very tight.
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Old 12-12-2016, 03:54 AM   #6
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Never heard of High resistance grounded systems before...

Did a google

https://www.mikeholt.com/mojonewsarc...g~20040812.php

HTH
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Old 12-12-2016, 06:38 AM   #7
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A starter bucket is a removable all in one motor controller, OCP (fuses or circuit breaker), control transformer (if needed, with line and load OCP) and the motor starter,

MCC's often have buckets that are plug in and sometimes though not always simple to remove without disconnecting any load or control conductors. Generally this is a feature on newer MCC's older MCC's the buckets were bolt -in.

High resistance ground systems have some advantages over grounded and ungrounded distribution systems.

With the system resistor sized fault current is kept low, which minimizes the impact of arcing ground faults, dead shorts allowing a facility to operate while the fault is located. AS in nan ungrounded system the "FIRST FAULT" is free as fault current is limited. ON the very few systems I have worked on the fault current was limited to 25 amps.

There are no phase to neutral loads allowed so transformers are needed for lighting (assuming you are using 277 or 120 VAC Lights) and any 120 VAC loads.

From IEEE 100 Disctionary
Attached Thumbnails
Test-resistance-grounded.jpg  

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Old 12-12-2016, 08:16 AM   #8
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Only disadvantage I can think of on an HRG system is that I believe the faulted part can assume a voltage well above earth potential which creates a shock hazard until the fault clears. But I've honestly never seen or heard of it happening, probably because the trip times on these systems are often very tight.
We did some work on a 600 Amp, 480 volt system and after cleaning all the gear, we re-energized and checked voltages, all were good. Once everything was energized, we found one phase was around 50 volts to ground. The other 2 were between 350 and 480 to ground.. Everything was operating normally. We went through breaker by breaker and found the one that was faulted. Verified it with a megger and eventually replaced the feeder.
Why was there no alarm? During the same shutdown time (but after we did our work), we had a testing company out to check the main breaker and some of the controls with it. When they looked further into the system, they found the NGR was pretty much destroyed. It was in rough shape and in need of replacement. The NGR alarm contacts were jumpered. Long before I got there. And sadly, to my knowledge, they still are. The client didn't want to spend the $3,000 on the parts and labour to fix it..
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Old 12-12-2016, 10:01 AM   #9
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We did some work on a 600 Amp, 480 volt system and after cleaning all the gear, we re-energized and checked voltages, all were good. Once everything was energized, we found one phase was around 50 volts to ground. The other 2 were between 350 and 480 to ground.. Everything was operating normally. We went through breaker by breaker and found the one that was faulted. Verified it with a megger and eventually replaced the feeder.
Why was there no alarm? During the same shutdown time (but after we did our work), we had a testing company out to check the main breaker and some of the controls with it. When they looked further into the system, they found the NGR was pretty much destroyed. It was in rough shape and in need of replacement. The NGR alarm contacts were jumpered. Long before I got there. And sadly, to my knowledge, they still are. The client didn't want to spend the $3,000 on the parts and labour to fix it..
If the controls have been messed with, that is a good reason there was no alarm.
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Old 12-12-2016, 10:29 AM   #10
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A starter bucket is a removable all in one motor controller, OCP (fuses or circuit breaker), control transformer (if needed, with line and load OCP) and the motor starter,

MCC's often have buckets that are plug in and sometimes though not always simple to remove without disconnecting any load or control conductors. Generally this is a feature on newer MCC's older MCC's the buckets were bolt -in.

High resistance ground systems have some advantages over grounded and ungrounded distribution systems.

With the system resistor sized fault current is kept low, which minimizes the impact of arcing ground faults, dead shorts allowing a facility to operate while the fault is located. AS in nan ungrounded system the "FIRST FAULT" is free as fault current is limited. ON the very few systems I have worked on the fault current was limited to 25 amps.

There are no phase to neutral loads allowed so transformers are needed for lighting (assuming you are using 277 or 120 VAC Lights) and any 120 VAC loads.

From IEEE 100 Disctionary
From this I gather that one disadvantage of HRG is the fact that transformer would be needed to run lighting circuits on a 480 system, adding to the cost of installation?

Advantage is to keep the plant running while the fault is located, and to keep fault current low so you protect equipment from arcing and burning.
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Old 12-12-2016, 10:40 AM   #11
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From this I gather that one disadvantage of HRG is the fact that transformer would be needed to run lighting circuits on a 480 system, adding to the cost of installation?

Ya it will add the cost but it depending on sizing on the system .

Advantage is to keep the plant running while the fault is located, and to keep fault current low so you protect equipment from arcing and burning.
Ya that is one main advantage about the HRG system but the only gotcha is phase to phase short that is only weak spot.
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Old 12-12-2016, 02:53 PM   #12
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From this I gather that one disadvantage of HRG is the fact that transformer would be needed to run lighting circuits on a 480 system, adding to the cost of installation?

Advantage is to keep the plant running while the fault is located, and to keep fault current low so you protect equipment from arcing and burning.
When working properly an HRG system may trip out rather than alarm.
When the main goal is to keep equipment operational after first fault so that a controlled shutdown can be done, a fully ungrounded system has advantages. AFAIK the biggest drawback of fully ungrounded is that an arcing fault can pump line to ground voltage well above line to line voltage.

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Old 12-12-2016, 03:30 PM   #13
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When working properly an HRG system may trip out rather than alarm.
When the main goal is to keep equipment operational after first fault so that a controlled shutdown can be done, a fully ungrounded system has advantages. AFAIK the biggest drawback of fully ungrounded is that an arcing fault can pump line to ground voltage well above line to line voltage.

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If the fault current to ground is limited, why would it trip the CB's in lieu of setting off the alarm?

I have heard this many times, do you know why?

Also I would add in reading about ungrounded systems this higher voltage can damage the insulation of other conductors.

Lastly just to clarify, in an ungrounded system EVERYTHING IS STILL BONDED, grounding is just as important as in a solidly grounded system. I have head a few electricians say they thought in a ungrounded system bonding and grounding was not necessary.
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Old 12-12-2016, 06:26 PM   #14
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If the fault current to ground is limited, why would it trip the CB's in lieu of setting off the alarm?

I have heard this many times, do you know why?

Also I would add in reading about ungrounded systems this higher voltage can damage the insulation of other conductors.

Lastly just to clarify, in an ungrounded system EVERYTHING IS STILL BONDED, grounding is just as important as in a solidly grounded system. I have head a few electricians say they thought in a ungrounded system bonding and grounding was not necessary.
Thumbsup on bonding!

The arc pumping effect, AFAIK, is a DC offset which results from an asymmetric spark gap acting like a very poor diode. But I might be wrong about that.
Like in a voltage doubler circuit to get really high voltage to ground.

If you only alarm and do not connect your detector output to s shunt trip or other interrupter, then you would not necessarily trip any OCPD. But with the HRG you will then have some fault current flowing in the EGC system continuously until shut off while with ungrounded you do not.

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Old 12-12-2016, 06:55 PM   #15
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T
If you only alarm and do not connect your detector output to s shunt trip or other interrupter, then you would not necessarily trip any OCPD. But with the HRG you will then have some fault current flowing in the EGC system continuously until shut off while with ungrounded you do not.

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I have seen that and also had a site where they put a bonding jumper on the main service, defeating the HRG.
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Old 12-12-2016, 07:43 PM   #16
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A resistance grounded system is an advantage because it limits the available current in a line to ground fault. And by placing a current transformer in series with the resistance you can use the transformer to trigger a relay protection scheme. Because the resistor is in the fault current path the current is reduced.

In an industrial situation with good maintenance this is a very good system. I have seen it used to protect a generator and MV cables UG at 7200 volts.
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