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Old 28th April 2010, 01:43 AM   #81
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Other than one or two points we generally agree. And the ones that we diverge are probably more the result of looking at different cases more than anything. Thanks for the well written answer.
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Old 28th April 2010, 02:33 AM   #82
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by smokinghot View Post
So by chance have you tested to see what voltage your utility is providing you? Are you going to design around peak usage of your neighbours or minimum...? My point is, for all you know the 1% voltage drop could be giving you 120v exactly at the equipment connection point. Or, you maybe even getting more than 120v.

Bashing your head against a wall over a 1% drop is a waste of time. You'll get greater variations during the day from the utility.

I suggested using 1% voltage drop, way up near the top of this thread not becasue anyone cares what the exact voltage is at the outlet or even what the drop is. But simply because "1% voltage drop" is a term his electrician can understand and he can look up in the NEC. Also it is something the building inspector can understand and check off..

The 1% is reasonably affordable goal too. What it gets you is a low impedance power outlet that has clean power He might also do an isolated ground but really a single outlet circuit is about the same effect. Either way the ground runs straight to the panel.

So just saying 1% drop dedicated outlet is all he needs to ask for. so all involved will know what he wants.
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Old 28th April 2010, 01:01 PM   #83
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This is basically where I'm at now.

The 'latest' plan is straight 10ga wire from a 20A breaker at the top of the panel to a dedicated (isolated ground either way) 20A 'hospital' outlet.

Would have already had the wire but last time I was at Homo-Depot the electrical aisle was a zoo...
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Old 28th April 2010, 10:00 PM   #84
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Hi Printer2,
They may send one phase to the local transformer, but we normally have two phases. There is 208 VAC (nominal) between them.
I think you mean 220V, Chris. In a 2 phase system such as found in houses, it's 220V (nominal) between phases. In a 3 phase commercial installation, there is 208V between any 2 phases.

The center tap of the power distribution transformer (the pole pig) is grounded at the pole and also at the service entrance. That center tap line becomes your neutral. From either "hot" line to neutral is 110~120V.
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Old 28th April 2010, 10:21 PM   #85
Pano is offline Pano  United States
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Default Ground rods.

There has been a lot of talk about NOT adding more grounding rods. And in the case of what the OP is doing, that's a good idea.

However - from my reading of the code, there are 2 cases in which you can and should add another ground rod.

1: If your ground does not meet the < 25 ohm requirement. Most don't. You are allowed to add extra rods to achieve the <25 ohm sink. But they must be 6' from each other and connected together. Thus they form one large ground point.

2: If your sub panel is in a remote building (garage, barn) and there is no ground or bonded return path to the main panel, a new ground should be installed at the remote location.

Case 2 is unusual these days, but is the case in my shop where 2 hots and a neutral where run, but no ground (circa 1954).

Code jockeys, please correct me if I'm wrong.
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Old 29th April 2010, 05:17 PM   #86
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Originally Posted by panomaniac View Post
1: If your ground does not meet the < 25 ohm requirement. Most don't. You are allowed to add extra rods to achieve the <25 ohm sink. But they must be 6' from each other and connected together. Thus they form one large ground point.

2: If your sub panel is in a remote building (garage, barn) and there is no ground or bonded return path to the main panel, a new ground should be installed at the remote location.
That is my understanding of the code as well.

A remote panel will not have the ground and neutral connected either; that ONLY happens at the service entrance.

I had toyed with the idea of a remote panel on the other side of the basement, but decided once this room is done, I will not have any unusual power requirements on that side of the house. The wood shop is in the same room as the panel now, so that's covered...
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Old 29th April 2010, 10:09 PM   #87
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To expand on the above posts:
a) In a remote building. The safety ground wire from the main building and the nearby ground rod will be connected to this building panel case or chassis. The neutral wire from the main building and all of this buildings neutral (white) wires will be connected to a terminal strip that is insulated from the panel chassis.
b) More ground rods are good, but all the main building ground rods are connected at only one point at that one point is near the AC Power Service Entrance.
c) The 25 Ohm Ground Rod Rule. It's difficult, it takes expensive test equipment and a lot of time to do test. So almost all residential electricians don't do the test, they just add more ground rods.
d) Ground Rods are mostly about safety when real bad things happen.
Noise just doesn't disappear down the Ground Rod wire.
If connecting to a ground rod makes the system quieter, then it's compensating for a wiring problem elsewhere.
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Old 30th April 2010, 02:18 AM   #88
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Hi Kevin,
Good points. I agree with yourself and panomaniac completely. It's important to note that the extra ground rods are considered as being one. The point occurs in one place only wired as a star between the commons and earth, or safety grounds.

Hi panomaniac,
You may be right about that. My education made a point about the 220V dryer socket being 208V instead of 220V. I had measured this to be true at and earlier point in time, but it may have been that the "110" circuit was actually 104 VAC instead of the nominal 117 VAC it is supposed to be. I'll measure my home outlets later to confirm.

-Chris
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Old 30th April 2010, 03:19 AM   #89
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Hey Kevin. Thanks for that. Very clear.

Chris. In any domestic system I've seen in the USA, it's 220 across the two legs. Or sometimes more. In every commercial venue I've done shows in, it's 208 across any two legs. I suppose because it's always 3 phase. This is something I see all the time because of the equipment we have to set up for shows.

It may be different in Canadaland. It certainly is different in Europe. In France we had 4 phase!
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Old 30th April 2010, 03:36 AM   #90
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in Germany we have 400V between two phases =voltage between phase and ground multiplied by rt(3). The should apply to all three phase systems with 120 angle between phases.
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