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PostPosted: May 4th, 2020, 10:36 am 
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Joined: January 15th, 2015, 7:19 am
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Location: Baltimore MD
thanks Pooge
this is what I thought


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PostPosted: May 4th, 2020, 10:45 am 
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Joined: July 9th, 2016, 7:23 pm
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Location: Fairfax Station, VA
Pelliott321 wrote:
thanks Pooge
this is what I thought


Sorry. I lied... The ground lug is usually connected to the metal mounting ears of the receptacle. As Stuart said, this would connect the ground lug to the chassis ground via the ears, and thus the safety ground, to cause a ground loop.


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PostPosted: May 4th, 2020, 11:01 am 
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Joined: January 15th, 2015, 7:19 am
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Location: Baltimore MD
ok I will look
if this is not the case I can insulate the socket mounting for now or when I get to it.


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PostPosted: May 4th, 2020, 11:05 am 
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Joined: June 22nd, 2013, 11:00 am
Posts: 791
Stuart Polansky wrote:
mix4fix wrote:
Whose bright idea was it to tie an entire room into a bathroom GFI?


I couldn't find the post to which you are referring.

GFCI receptacles installed in bathrooms are to have no outlets outside of bathrooms connected to them.

Does this help?

Stuart


It was a rant. My bedroom is connected to the bathroom GFI.


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PostPosted: May 4th, 2020, 11:10 am 
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Joined: July 9th, 2016, 7:23 pm
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Location: Fairfax Station, VA
Pelliott321 wrote:
ok I will look
if this is not the case I can insulate the socket mounting for now or when I get to it.


Technically yes, but why bother? You'd also have to use non-conductive screws.

Another change I'd make is to not wire your receptacles in series to the supply wires. Run pigtails from each receptacle to a common connection at the power feed: i.e., in parallel.


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PostPosted: May 4th, 2020, 11:17 am 
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Joined: July 9th, 2016, 7:23 pm
Posts: 27
Location: Fairfax Station, VA
mix4fix wrote:
Stuart Polansky wrote:
mix4fix wrote:
Whose bright idea was it to tie an entire room into a bathroom GFI?


I couldn't find the post to which you are referring.

GFCI receptacles installed in bathrooms are to have no outlets outside of bathrooms connected to them.

Does this help?

Stuart


It was a rant. My bedroom is connected to the bathroom GFI.


LOL! Years ago when I bought a townhouse, and GFCI outlets were dear, they wired my back yard outlet to the one in the master bathroom on the second floor! Took me a while to find out why the plug for my electric lawnmower went out. GRRRR! Nothing like having to take off wet muddy shoes while mowing to walk upstairs to reset it!


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PostPosted: May 4th, 2020, 11:21 am 
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Joined: January 15th, 2015, 7:19 am
Posts: 1226
Location: Baltimore MD
ok I looked and they are not gound isolated
I will order some and make the changes
Just curious with the short distances what is wrong with the series connection


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PostPosted: May 4th, 2020, 11:28 am 
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Joined: January 15th, 2015, 7:19 am
Posts: 1226
Location: Baltimore MD
ordered 6 S&P hospital grade (Red) isolated ground receptacles
be here in a week


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PostPosted: May 4th, 2020, 12:40 pm 
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Joined: July 9th, 2016, 7:23 pm
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Location: Fairfax Station, VA
Stuart Polansky wrote:

I see now that you have paralleled the output windings. No sweat, but now you must make a ground connection, since this is a separately derived system. The rule is, at the SOURCE of the separately derived system (that is, within the isolation transformer enclosure) you must bond together the grounded and grounding conductors: the white and the green. So, you've used the brown and orange leads as your neutral. 1) Mark them with white tape, to indicate a neutral. 2) Connect a green set of conductors to the brown/orange connection and connect them to the receptacle ground pins. Disconnect 3) Disconnect the building grounds from the receptacle ground pins (that being the green wire from the power cord. 4) Connect a green or bare wire from the green/brown/orange splice to the grounding electrode system in the house. You can make this connection using a ground clamp on the cold water pipe, close to the existing clamp; in the main circuit breaker panel, on the bonding jumper (neutral bar), or spliced with a split bolt connector (commonly called a "bug"), right onto the grounding electrode conductor (wires running from the circuit breaker panel to the grounding means (rods, cold water, etc.)

All of the above is a must and the only challenging part should be the long wire to "ground".


Stuart, I'm not sold on your requirement to have a second ground on the secondary side run all the way back separately. While that would be ideal, I don't think it is a code requirement. What store-bought isolation transformer does this? I would do it if I could, but I don't see it as a "must" do. Bonding the grounded (neutral) and ground on the secondary side, and connecting that bond to the power cord ground, would appear to meet this requirement, at least as far as code.

So instead of connecting the secondary ground to a water pipe, it could be connected to the ground on the primary side. It's the same reference, code wise.

Yes, it's not as good, because there may be more ground noise voltage on the secondary by connecting the secondary ground to the power cord ground.

However, it would help to mitigate some of the inherent ground voltages on the secondary ground resulting from ground currents on the primary side:

1) This one doesn't cost anything. Disconnect all grounds from the chassis. Probably best to disconnect the filter and connections to the receptacles as well. With the transformer powered up, measure the voltage between the detached ground wire in the power cord and the chassis. Reverse the hot and neutral wire connections to the transformer primary and measure again. Wire the transformer for the lowest measured voltage. (Depending on the coil orientation in the transformer, it will induce a current in the chassis that feeds into the ground. So, connect the primary orientation for the least voltage from the power cord ground to chassis. BTW, do this for amps and pre-amps, dacs, etc., too, if they have a three-prong plug.)

2) Move the filter out of the transformer box, to a point closer to your circuit breaker box. This will shorten the ground conductor from the filters for less voltage on the reference do to noise currents. You would need it in a separate chassis, and hardwired to the CB box and hardwired to the cable run to your isolation transformer. Alternatively, move the combined filter and isolation transformer chassis close to your CB panel. This may not keep noise out of the run from there to your hi-fi equipment, but the bulk of the noise comes into your service entrance, anyway, and your ground would be cleaner, being shorter.

If 2) is done, put all the receptacles in another chassis near your hi-fi equipment. Tie each receptacle ground individually to a star ground in the chassis with the power cable ground.

I did not see a fuse in your chassis. You should definitely put one at the power cord entrance!!!! This should be rated no more than the current rating of your transformer.


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PostPosted: May 4th, 2020, 1:53 pm 
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No doubt Pooge, the requirement depends on the installation. Just had this discussion with Tom P.

I think the worst overall solution is connecting the line-side power cord ground to the secondary ground of the isolation transformer, from a noise standpoint. I could be wrong, but using the household circuit grounding conductor just seems like it might be an antenna for noise, given all that would be connected to an un-dedicated circuit. I could be wrong.

Of course, the secondary could be left floating; an ungrounded system. As you know, this can be done for a variety of reasons (welding, operating rooms, etc.). But my concern is a practical one. This is not an installation where only supervised personnel have access (like an industrial plant). Hey, the guys come over, someone brings his latest pride and joy, no additional outlets on the IT, so it gets connected to line-side house power, and the interconnects "ground" the secondary. Everyone has knocked back an adult beverage or two.....Best case, it just makes noise. Worst case, well, one of our customers exploded three brand new computers because the printer was plugged-in across the room, and one receptacle was wired in reverse polarity. Now, you'd think after the second one blew up..........

Not saying this will happen, but decades at this has made me cautious. I wouldn't recommend an ungrounded system in a residence, but for exceptional circumstances.

My thought was that running a clean, insulated ground back to the service ground would be the least likely route to introduce noise in the system.

As to Code requirements for grounding an isolation transformer, I'll have to read up. Since this is a cord-and-plug connected appliance, not part of the building electrical system, the only Code rules that might apply are that of complying with the UL listing.

When we hard-wire install a transformer in a building, the inspectors always ensure we have grounded the transformer to the service ground.

You bring up excellent points. Great ideas there!

Stuart


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