Earth Ground opinions

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vanweld
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Earth Ground opinions

Post by vanweld »

Just looking for recommendations on earth grounding. Been searching all day and can't really get a locked down answer. Table functions and cuts anything 1/4" and up nearly perfect (clean, slight angularity if any, next to no dross). However, trying to cut 14ga or 16ga the gremlins come out. 14ga with some hold down weights, I can get one or two of my 8 piece nest cut and then the plate warps very slightly and I drag the plate/crash the torch. One piece cut at a time and I can make it work but I just don't believe my height control is working correctly. When I do the light bulb test on my earth ground, I initially had 74 volts! Not 0.74, 74. I did not have the right stuff to do this test when I first set the table up, got excited to try it and just went forward. I soaked the rod with water down the hole and got it down to 43 volts. Can't get any better. Main question is would it be best to weld/couple more rods onto this and drive one rod deeper or install multiple rods. I have heard multiple rods need to be anywhere from 3ft to 10ft apart. I am good with either way, but want to get some feedback so I hopefully get a resolution quickly. Been raining/snowing here is SC for a couple days, so I was kind of surprised that the water down the hole help. Would assume the ground is pretty saturated. Shop Sabre sidekick table, hypertherm PM85, single 8 ft ground rod. If any other info is needed, let me know and thanks in advance for all the help.

Brian
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Re: Earth Ground opinions

Post by acourtjester »

A few thing are you connecting the work lead from the hypertherm directly to the metal being cut. Another thing is the work lead from the hypertherm is not ground it is at a positive potential. By height control are you using a torch height controller which senses the arc voltage to adjust the torch cutting height after the torch starts to cut. A floating head switch or ohmic sensor are not the same thing, they are only to find the metal surface at the start of the cutting operation so the pierce height is correct.
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vanweld
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Re: Earth Ground opinions

Post by vanweld »

Have not tried connecting directly to the work yet. Manual said to connect to the point on the table. They gave instructions on how to do the lightbulb test but I just didn't have the stuff to do it so I skipped it and thought all was well. Started seeing some issues and decided to run the test and found the high voltage indicating a bad earth ground. I will hook it back up and test the clamp to the work piece. Table has OHMIC sense and reads the voltage to control torch height. You can visually see it drops to sense work piece, raises to pierce height, and drops to cut height. During cutting it doesn't appear to be adjusting. This has not been an issue on thicker material where there is essentially no warpage.
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Re: Earth Ground opinions

Post by acourtjester »

From what you say it may be the torch height controller as it should follow the metal surface by using the arc voltage. Some unit have a test function where it will send the signals to the computer for arc Ok, up, and down and it shows on the units lights. If you are running Mach 3 you can look on the diagnostic page and see the signal indicators also changing. Another thing if you are not setting the correct arc voltage it will not track as it should.
Here is a video I recorded showing how to check and setup a THC unit, they are not all the same but the basic functions are the same and you should get the idea.
https://youtu.be/EyZJVMtzKzY
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Re: Earth Ground opinions

Post by robertspark »

vanweld
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Re: Earth Ground opinions

Post by vanweld »

I am doing the light buld test. I have driven to nearly 20’ and the best reading I can get is 24 volts. Been adding water down the hole as I drive.
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Re: Earth Ground opinions

Post by vanweld »

Robertspark,

Thanks for the fluke article. Good info! I am planning to follow that exact hypertherm article but seem to be stuck on step one with the ground rod
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Re: Earth Ground opinions

Post by robertspark »

How are you reading 24 volts???

24v between what and what??

Is this any help?

http://www.rogerhalstead.com/ham_files/ground.htm

Pouring water down a hole to improve conductivity is not good as it won't remain that way
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Re: Earth Ground opinions

Post by vanweld »

When doing the lightbuld test I am seeing that voltage between the neutral on the circuit and the ground rod. I am hooked up per every diagram I have found for this test. Understood on the water, just wanted to see if it would make a difference.
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Re: Earth Ground opinions

Post by robertspark »

It sounds to me like you have an unsafe installation given neutral should be at the same potential difference (voltage) as the earth.

BIG POINT OF NOTE.... I am in the United Kingdom.... I have however been an electrician in various countries in southern Africa too.... So I do not know or understand your local electrical customs..... I would suggest asking on an electrical forum that may deal with your locality....

America "seems" to like to use delta wound transformers which have a center tap to provide a neutral.... That way you get 220v phase to phase (hotwire <> hotwire) and 110v phase to neutral (hotwire <> centertap).

The thing is.... I think the center taps are supposed to be connected to a central point at the transformer and then this is then grounded so that you only have two voltages possible..... 220v and 110v....

By having a neutral at 70 or whatever volts above the ground you have an neutral fault to me

Such as this

https://i.stack.imgur.com/Lwzfr.png

This thread may be of help to you too.... But I would suggest consulting a local electrician too who understands your local wiring regulations and how the supply is wired locally.

https://electronics.stackexchange.com/q ... ne-voltage
Last edited by robertspark on Mon Dec 10, 2018 3:44 pm, edited 1 time in total.
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Re: Earth Ground opinions

Post by robertspark »

Adding more earth / ground electrodes will not fix a broken neutral fault.

Again... IMO YMMV ....
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Re: Earth Ground opinions

Post by vanweld »

I am not getting any faults using an outlet tester. What other ways to check for a neutral fault?
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Re: Earth Ground opinions

Post by robertspark »

The voltage on the neutral line should get higher the greater the load you place on it. (If you have a fault)

So.... say you have nothing running.... the current flowing from a hot (live) wire to the neutral will be very low (leakage current only) so the voltage should be very low.

if you now turn on an electric cooker, loads of lights, compressor, plasma cutter welder whatever you should see the voltage at the neutral rise relative to earth and your voltage from phase <> live (hot wire) will narrow (drop).

If it were me.... I would try to turn off everything (main switch) and measure the voltage from
Live to live (if you are in the usa {or on a 2-phase system...}
Live to neutral (both of them if you are in the USA)
neutral to earth / ground.

In the UK we use an earth impedance tester .... or a tester that can test the earth loop impedance
http://www.sparkyfacts.co.uk/Inspection ... e-Test.php
You can use it to test Re / verify it is as low as expected {the allowable expectation changes relative to the system and different locality in the world}

PDF page 24/25 can give you an idea how such a meter does it (I have one of these, now been superseded)
https://www.industrialcalibration.co.uk ... 0Guide.pdf

If you don't have the tester....

I would make sure no one else is in the vacinity.... {you have a controlled environment for testing}

I would then attempt to put the system under a known load (electric kettle (3kW), tumble dryer (3kW).... compressor. (3kW) .... check the name plate ratings.... get the total connected load )...

Then take all the voltage readings again.... when the system in operating under a known load (open the air valve on the air compressor so it gives a fairly good run period to allow you to take the readings).

Given you know what the load was and what the voltages (Phase>phase, phase> neutral, neutral > earth etc) under test was you can work out what the resistance of the neutral is ...... and therefore possibly where your fault is .....

You may have a fault internal to your premises (more likely) or it may be external (transformer / mains side). {it is only more likely because you or someone may have changed something internally.... the supply does not change very often.... but I have seen neutral faults a few times supply side, but they are rare .... and are normally a cable, transformer or termination fault over time}
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Re: Earth Ground opinions

Post by islander261 »

The issue of neutral potential relative to safety ground can be difficult in the US with old or rural locations. The relevant code has changed over the years and once good bonding may have deteriorated over time or be completely lacking.

You should contact your utility and have them check your supply at the service entrance for any faults, they should do this for free if you let them schedule the work. If the fault is in your premise wiring then you need to get a licensed electrician to sort it out. This is a common cause of electrical fires. Be warned that your usual home owners or business insurance will not cover damage if they suspect that electrical work was done without permits/inspections or not done by a licensed electrician. If you want to run a plasma cutter you should consider having all the neutral bonding and safety ground connections brought up to the current code.

John
vanweld
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Re: Earth Ground opinions

Post by vanweld »

So, long story. Drove a ground rod, had a bad result on the light bulb test. Welded on two more 8ft rods and drove them in. I am now 20ft in the ground. I had to cut some off to drive because of low ceiling height. Anyway, I get a bad reading on the light bulb test. If I remember right the best I could get was 25 volts. Added on the cutoff pieces just because. Tried to drive and ended up breaking the weld about 2ft underground. Not happy. Started over. Drove an 8ft rod, had a dim bulb during the test and measured 74 volts. moved 10ft away and drove second rod. Tied them together and now have 62 volts and bulb slightly brighter. Drove 3rd rod 8 ft in the opposite direction of the original. Tied them together with #4 stranded ground wire. Now at 54 volts while doing the light bulb test. Went to test the ground rod on the service panel for the house using the exact same light bulb test. Hooked it up and the bulb glows full strength. Getting 0 to 0.1 volts on the meter. Really mad now. Shop is on a separate feed from the house. There is a split at the meter for the house and a feed going to the detached garage. Kind of at a lose on this one. My shoulder is now too sore to keep driving ground rods in with a sledge hammer and the budget is in fear of how many rods I will have to tie together to make this work. Has anyone ever used GEM for a grounding rod? I am thinking of going this route to try to solve my issues but wanted some feedback before purchasing the product.

Thanks in advance.
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Re: Earth Ground opinions

Post by robertspark »

You are dealing with parallel resistances

1/z =1/a +1/a +1/a etc

Given the ground resistance is all roughly the same it works as follows

Say 1 rod is 25 ohms
2 rods will be roughly 12.5 ohms
3 rods will be 8.33 ohms
4 rods will be 6.25 ohms
5 rods will be 5 ohms etc
6 rods will be 4.166 ohms
Etc

No I don't know why your light bulb tests go from 74v, 62v, 54v as there should have been a bigger jump from 1 to 2 (1/2) and then scaled less of a drop

Given your utilities / electrical supplier connection is fine. I would suggest checking your cable continuity from the service head to the garage..... Sounds like you may need to run a new cable in as that may be your problem.

From your service head do you not have or run a 3 core cable to the garage? (L+N+E)... Or a 4 core cable.... (L1+L2+N+E) Or one with an external "cpc' (circuit protective conductor)
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Re: Earth Ground opinions

Post by islander261 »

It sounds like a bad connection in the safety ground or neutral conductor between the service entrance and the garage. This is common because old code allowed the neutral safety ground connection to be made through the conduit/box flanges at the service entrance without any corrosion protection. This is a common problem. The current code requires that 4 conductors be run to the remote panel L1, L2, neutral and PE. You really should hire a licensed electrician to sort this out.

John
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Re: Earth Ground opinions

Post by vanweld »

There is a 4 wire connection from the meter to the panel in the garage. L1, L2, L3 and PE.
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Re: Earth Ground opinions

Post by robertspark »

Now that is interesting.... I didn't know it was three phase... Are you sure it is L1 L2 and L3

No neutral?

How do you get neutral in the house?
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Re: Earth Ground opinions

Post by vanweld »

It is not. My mistake. 2 hots, 1 neutral and 1 ground. Typing faster than i was thinking.
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Re: Earth Ground opinions

Post by robertspark »

Have you tested the continuity?
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Re: Earth Ground opinions

Post by vanweld »

Did a continuity check at the panel in the garage. Had the power shut off to the garages. All had good audible tone on the meter.

Neutral to ground- 0 ohms
L1 to ground- 2 ohms
L2 to ground- 1 ohms
L1 to neutral- 3 ohms
L2 to neutral- 2 ohms

Did not have long enough leads to test the length of cable from the house to the garage. Not sure if that would be necessary?
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Re: Earth Ground opinions

Post by WyoGreen »

I suspect you didn't turn off the breakers in the garage with those readings. You should read infinity from the hots to ground or neutral at the garage panel with the breakers off. In that situation it would be bad to read continuity from the hot leads to ground, because that would indicate a short in the cable running from the house to the garage. The readings you got I suspect are thru equipment left plugged in at the garage.

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Re: Earth Ground opinions

Post by MARK2MAHAN »

Where in SC are you ?
Im in the upstate, I have same issue.
Ive driven 11 , 8' rods in , 4 of them to 16'.
Most are parallel, 3 in series.
Even got into septic system in hopes of better soil.
And i did tear my shoulder putting them in & had surgery , still in recovery...
I started at 74 volts and now down to 5.
Tech support told me to give it a try...
Which i hope to this weekend...
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Re: Earth Ground opinions

Post by robertspark »

? Think you rose from the dead an old post
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