CKT WIRE COUNT

[haskindm]

Could there be an any bigger waste of money than pulling 10- IG's for 10 circuits? :roll:

If IG is required then it is not a waste. On a properly installed electrical system (no ground loops) then ALL IG circuits are a waste. If it is needed because of poor installation/maintenance then it is needed regardless of the number of circuits.

 

[haskindm]

We recently did a project where they specified IG outlets to be mounted on an audio amplifier rack. Problem is, they also required those circuits to be installed in metal conduit.

AS soon as the audio amps were plugged in, the IG was physically connected to the building ground VIA the metal casing of the amps. Complete waste of money and resources.

But it made them feel good to have all those (non-)IG circuits in there!

ALL IG CIRCUITS SHOULD BE INSTALLED IN METAL CONDUIT or with a separate non-IG ground. The whole purpose of IG is that you have a "clean ground" that is taken through any sub-panels and connected to the neutral/ground at the main service for "sensitive electronic equipment". The other ground (conduit or non-IG ground wire) is used to bond the conduit, boxes, and yokes and may be terminated in the sub-panel (panel-board). On an IG receptacle the equipment ground prong is "isolated" from the yoke, thus the term "isolated ground". The yoke, box conduit, etc must still be grounded using some sort of non-IG ground.

 

[haskindm]

Yeah, I have an ongoing argument with an Audio subcontractor. He insists that an isolated ground for his audio equipment is an isolated wire run to an isolated bus in the panel, and then a 3/0 to a ground rod isolated from other grounds. He insists that prevents hum in his audio system. I have argued with him until I am blue in the face, and he still believes that. I believe, I will never provide him with what he is asking for.

The most common mistake I see is that an Engineer only cares that he has a dedicated redundant ground back to the source sub panel.

It will often reduce noise, but at the risk of having a system with no ground fault return path. If a line to ground fault occurs, the separate ground rod will not carry enough current to trip the breaker so the EGC and the ground rod become energized. What he really needs is a isolating transformer for his equipment (or better equipment), but that costs him money. It is cheaper to install an unsafe system! All he cares about is the lack of hum.

 

[kwired]

If you can believe that isolated ground outlets are connected using isolated grounds then there is a lot of isolated grounds being used in retail, cash registers, etc.

Some are truly isolated, some are not. Most cases depends on how smart the installer was, sometimes somebody is more concerned with having the orange receptacle designated for the cash register than they are about how it is grounded.

If you are concerned that unwanted signals may be induced into the Hot, Neutral, Grounding triplet, then you might use individual neutrals and individual isolated ground wires for each circuit as a twisted triplet (like a twisted pair). But this approach would only make sense if you were immensely paranoid.

I 've always been in favor of shared neutrals and shared grounds.

Always been my thought, they are all shared at the feeder and service level anyway, why is a shared neutral at the branch circuit level all of a sudden not a good thing, but is just fine for a feeder or service?

ALL IG CIRCUITS SHOULD BE INSTALLED IN METAL CONDUIT or with a separate non-IG ground. The whole purpose of IG is that you have a "clean ground" that is taken through any sub-panels and connected to the neutral/ground at the main service for "sensitive electronic equipment". The other ground (conduit or non-IG ground wire) is used to bond the conduit, boxes, and yokes and may be terminated in the sub-panel (panel-board). On an IG receptacle the equipment ground prong is "isolated" from the yoke, thus the term "isolated ground". The yoke, box conduit, etc must still be grounded using some sort of non-IG ground.

If you have no metal raceway, metal sheathed cable, or metal outlet box what else is there to ground Besides the yoke of an IG receptacle? Is the yoke itself going to cause problems if it is connected to the IG and nothing else?

 

[hillbilly1]

?.............. I've seen every kind of IG installation you can think of... including IG's tied to a non-GES ground rod. :happyyes:

My favorite is where they truly do isolate the ground, insulated ground bar, isolated grounds tied to it, but no ground tied to the bar. That happens far too often.

 

[haskindm]

If you have no metal raceway, metal sheathed cable, or metal outlet box what else is there to ground Besides the yoke of an IG receptacle? Is the yoke itself going to cause problems if it is connected to the IG and nothing else?

IF an installation is as you describe above you should NOT use an IG receptacle. You already have an isolated ground assuming the ground wire originates at main service, and you will need to find a way to bond the yoke of the receptacle as it is NOT connected to the isolated ground.

 

[kwired]

IF an installation is as you describe above you should NOT use an IG receptacle. You already have an isolated ground assuming the ground wire originates at main service, and you will need to find a way to bond the yoke of the receptacle as it is NOT connected to the isolated ground.

I know, my point is why install IG receptacle and/or IG conductor in the first place if there is nothing that requires grounding besides the grounding terminal of the receptacle? There is nothing to isolate. Put in a real IG receptacle and now you have a yoke that needs grounded, is it worth running a second equipment grounding conductor just for grounding the yoke that likely is not causing any troubles in the first place?

 

[kbsparky]

ALL IG CIRCUITS SHOULD BE INSTALLED IN METAL CONDUIT or with a separate non-IG ground. The whole purpose of IG is that you have a "clean ground" that is taken through any sub-panels and connected to the neutral/ground at the main service for "sensitive electronic equipment". The other ground (conduit or non-IG ground wire) is used to bond the conduit, boxes, and yokes and may be terminated in the sub-panel (panel-board). On an IG receptacle the equipment ground prong is "isolated" from the yoke, thus the term "isolated ground". The yoke, box conduit, etc must still be grounded using some sort of non-IG ground.

Which is exactly what we did.

So what happens to the "isolated" ground when they plug in those audio amps? You know, the ones with the 3-prong cords that just happen to have the grounding conductor bonded to the metal frame of the amp? Then those amps are bolted into the metal racks to look nice and neat. The same metal racks that they wanted me to mount the metal 1900 boxes to, which are bonded to the non-isolated metal conduits. The same metal conduits that are strapped to those metal racks (get the picture now?) ....

Is there any REAL benefit when they are plugged in now?

 

[ActionDave]

.... sometimes somebody is more concerned with having the orange receptacle designated for the cash register than they are about how it is grounded.

If even that.

I just worked on a store. Specs called for an IG circuit for the cash wrap so we ran one. The cash wrap arrived pre-wired with plain old CR-20 recpts. Oh well. We got paid for the extra wire in the home run. I doubt there will be any problem with the register.

 

[Strathead]

If IG is required then it is not a waste. On a properly installed electrical system (no ground loops) then ALL IG circuits are a waste. If it is needed because of poor installation/maintenance then it is needed regardless of the number of circuits.

I think you miss the point. That is 10 IG wires in ONE conduit and that is a waste of the 10th magnitude.

 

[Strathead]

ALL IG CIRCUITS SHOULD BE INSTALLED IN METAL CONDUIT or with a separate non-IG ground. The whole purpose of IG is that you have a "clean ground" that is taken through any sub-panels and connected to the neutral/ground at the main service for "sensitive electronic equipment". The other ground (conduit or non-IG ground wire) is used to bond the conduit, boxes, and yokes and may be terminated in the sub-panel (panel-board). On an IG receptacle the equipment ground prong is "isolated" from the yoke, thus the term "isolated ground". The yoke, box conduit, etc must still be grounded using some sort of non-IG ground.

This is not really true, and it is the misconception that causes a lot of the problems. The IG is there to provide a "0" reference voltage for equipment that uses various voltages in its operation. The stray voltage potential between the neutral and the ground that you get in a normal system is what this equipment is sensitive to. It is no more a grounding wire than a neutral is.

 

[kwired]

This is not really true, and it is the misconception that causes a lot of the problems. The IG is there to provide a "0" reference voltage for equipment that uses various voltages in its operation. The stray voltage potential between the neutral and the ground that you get in a normal system is what this equipment is sensitive to. It is no more a grounding wire than a neutral is.

Whether isolated ground or not, put a load on the neutral and you have voltage drop over the length of that neutral. You will have a voltage between neutral and ground if you have a voltage drop on the neutral. How much voltage will depend on size of conductor and amount of load.

I can see N-G voltage potentially being a problem - but I don't see isolating the ground as being anything that will correct that problem.

 

[Strathead]

Whether isolated ground or not, put a load on the neutral and you have voltage drop over the length of that neutral. You will have a voltage between neutral and ground if you have a voltage drop on the neutral. How much voltage will depend on size of conductor and amount of load.

I can see N-G voltage potentially being a problem - but I don't see isolating the ground as being anything that will correct that problem.

It is not ground. That was my major point. It doesn't care what the voltage potential is between it and the neutral. It cares what the potential difference is between the hot and the bonding point at the source! I believe, (pretty sure) that is this type of equipment uses various voltages, +3, -5, -3 etc. to indicate different stuff. When they needed IG often it was that this equipment was sensitve to the stray voltages. I don't know how to explain it any better.

 

[kwired]

It is not ground. That was my major point. It doesn't care what the voltage potential is between it and the neutral. It cares what the potential difference is between the hot and the bonding point at the source! I believe, (pretty sure) that is this type of equipment uses various voltages, +3, -5, -3 etc. to indicate different stuff. When they needed IG often it was that this equipment was sensitve to the stray voltages. I don't know how to explain it any better.

I'm not all that up to speed either on what goes on in this equipment, but it is more than just voltage between hot and ground also. What happens to +3 volts if the supply voltage changes from 123 to 118 because extra load was added to the service yet that change of supply voltage is considered acceptable?

I think that they just have better designs with todays equipment is part of why this is not as big of an issue than it used to be, (and also part of why I am no longer up to speed with the information related). I think most problems happened where there was communications between two (or more) devices that used a grounded shield and there would be currents on that shield that caused problems. Today most of the equipment now uses unshielded communications or even wireless communications. Anything that uses a shielded cable (like maybe USB) is short in length and not subjected to the same conditions that caused problems in older equipment

 

[fmtjfw]

RS-232 connections (serial lines) on computers are signals referenced to a common point. The 25-pin version has a common wire and a shield wire. In the 9-pin version the shield and common are one and the same. In practice, even in the 25-pin version, the two were often connected together. This meant that the common voltage reference was often forced to the power ground of each end of the circuit. Since the power grounds were typically orders of magnitude more conductive than a long common wire, if they differed they could corrupt the signals.

More modern computer connections (twisted pair Ethernet, USB, SATA) all use balanced signaling (a + and - for each signal)
Older connections (RS-232, ATA, Centronics) used multiple signals to a common (ground) wire.

 

[Strathead]

RS-232 connections (serial lines) on computers are signals referenced to a common point. The 25-pin version has a common wire and a shield wire. In the 9-pin version the shield and common are one and the same. In practice, even in the 25-pin version, the two were often connected together. This meant that the common voltage reference was often forced to the power ground of each end of the circuit. Since the power grounds were typically orders of magnitude more conductive than a long common wire, if they differed they could corrupt the signals.

More modern computer connections (twisted pair Ethernet, USB, SATA) all use balanced signaling (a + and - for each signal)
Older connections (RS-232, ATA, Centronics) used multiple signals to a common (ground) wire.

Excellent explanation thank you. To tie it back to the main discussion, the isolated ground is in fact a reference wire to the bond, not a graounding wire because of the above.

 

[Smart $]

Excellent explanation thank you. To tie it back to the main discussion, the isolated ground is in fact a reference wire to the bond, not a graounding wire because of the above.

There are many "theories" on the reason for and application of IG circuits. From what I recall, the reason IG's are permitted in the NEC is none of the above. Everything mentioned so far in this thread can be served with solid, redundant, and low-resistance grounding methods, including providing a steady-state voltage reference.

The NEC initially permitted isolated grouunding for the purpose of mitigating RFI/EMI. Older electronic gear emitted a lot of RFI compared to modern equipment. In order to mitigate widespread RFI, shielding techniques were employed in the equipment. Just as many communications wires are shielded to prevent influence from external stray signals, the same rationale also serves to mitigate the external spread of RFI generated from within. The [conductive, metal] shielding utilized in that equipment was connected to ground.

Going back in time a bit more, it was tied to the neutral upon the advent and use of the polarized two-prong plug and receptacle. Any of you ever opened up an old tube-type TV or amplifier? What wiring could be, was done so within the "chassis", a prime example of shielding to mitigate the spread of RFI.

The one application which has been correct thus far is "ALL IG CIRCUITS SHOULD BE INSTALLED IN METAL CONDUIT". The reason is, it has been found that connecting the equipment shielding to any conductor can in effect cause it to act as an antenna, which is actually the opposite of all intents and purposes. Running the IG circuits in metal raceway (i.e. includes metal conduit and tubing ) acts to shield the IG "drain" wire. There is no requirement for running IG circuits in metal raceway, but if using a non-metallic wiring method, that is taking the risk of having an antenna-effect IG wire.

Wrong or right, you guys now have my two-cents worth on the matter. :angel:

 

[kwired]

.... graounding wire ....

There is a term I am not familiar with

 

[Strathead]

There is a term I am not familiar with

:slaphead:

 

[ddderek]

Hire an Electrician!... this isn't Home Depot!

Hire an Electrician!... this isn't Home Depot!

All due respect, isn't this electrical wiring 101?

Exactly... LOL... Is this the electrical aisle at Home Depot or something???

Hire a LICENSED ELECTRICIAN, he'll know how many wires you need AND how many turns to turn the wire nuts!!