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Author Topic: Changing power cord on Hallicrafters S-38  (Read 6194 times)
W2JUV
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Posts: 9




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« Reply #15 on: April 18, 2013, 07:51:53 AM »

This is my 2-cents worth and I may be repeating some points already made but here goes.  Many of these old radios have a bypass capacitor connected from one side of the AC cord to the metal chassis.  The intended purpose is noise filtering, and it will be wired in before the power xfmr if there is one. Have seen several links here that detailed correct replacement part and process if you decide that is necessary.  Should you decide to install a 3-wire cord, make sure the black (hot) wire is interrupted by the OFF/ON switch.  The green wire(electrical service ground) goes to the metal chassis.  The white wire(electrical neutral) will connect to power to same point as original.  DO NOT connect white and green wires together.  Also if a 3-wire cord is installed, remove and discard the AC line bypass capacitor as it draws enough currret to trip a GFI receptacle/breaker as soon as the radio is turned on.  My personal preference is replace the original cord with a polarized type, check and/or replace the bypass cap. 
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N3DT
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« Reply #16 on: April 18, 2013, 04:05:10 PM »

Well, the white and green wire is connected together back at your 'modern' entrance panel, so I'm not sure what can be done about that.  I have an S-38E and I'm not sure how I'm going to hook it up. I'll get there when I get there.

Dave
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AA4PB
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« Reply #17 on: April 18, 2013, 04:24:17 PM »

The primary service entrance panel is the ONLY place that code permits and requires that the ground and neutral be connected together. The idea is that the grounding conductor only carries fault current in the event of a short. If you connect the ground and neutral together at the device then the load current will be split between the neutral and the grounding conductor. That means that the case or chassis will be at a slightly different voltage than the other grounded devices in the house - a potential shock hazard.
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KD0REQ
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« Reply #18 on: April 18, 2013, 06:09:05 PM »

it is also theoretically possible that if there is a neutral fail someplace, line current will look for a path to ground wherever it finds one.  if there is 0.21 ohm in the direct neutral, and the next lowest resistance to ground is 0.24 ohm through the S-38 neutral to chassis to ground, you put whatever power that other device draws through the wiring of the line cord to the Halli.

this can be double-plus ungood.

that's why the only junction of neutral and ground occurs at the entrance panel, which by code should also have two paths to earth ground on opposite sides of the building.  typically in a home, one is the ground rod, the other is the cold water pipe if you have metallic plumbing.
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K1CJS
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« Reply #19 on: April 19, 2013, 04:14:18 AM »

...that's why the only junction of neutral and ground occurs at the entrance panel, which by code should also have two paths to earth ground on opposite sides of the building....

Two paths?  Maybe by your local code, but not by the NEC.  AAMOF, some local codes prohibit connection to a water pipe if the water system has any plastic pipe used in it.  The reason for that is that a ground strap on a copper pipe that is NOT grounded can well put an electrical potential on the home water system--including faucets and other plumbing fixtures.
« Last Edit: April 19, 2013, 04:18:05 AM by K1CJS » Logged
AA4PB
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« Reply #20 on: April 19, 2013, 07:08:59 AM »

I believe the NEC prevents the USE of the water pipe AS THE GROUNDING CONDUCTOR if it contains any plastic. You are not prevented from bonding the conductive plumbing pipe to the electrical system ground. If, for example, you have copper water pipes in the house but have a plastic pipe or coupling going to the street or well then you are still required to bond the conductive pipe to the electrical system ground. That prevents the water pipes from every being energized to a different potential than the electrical system ground. The electrical system is required to have a grounding conductor that goes to a ground rod.

Years ago when most plumbing included conductive pipe running underground you were premitted to use that pipe as the grounding conductor for the electrical system. You can no longer do that in most places.
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K1CJS
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« Reply #21 on: April 20, 2013, 10:37:10 AM »

I believe the NEC prevents the USE of the water pipe AS THE GROUNDING CONDUCTOR if it contains any plastic. You are not prevented from bonding the conductive plumbing pipe to the electrical system ground. If, for example, you have copper water pipes in the house but have a plastic pipe or coupling going to the street or well then you are still required to bond the conductive pipe to the electrical system ground. That prevents the water pipes from every being energized to a different potential than the electrical system ground. The electrical system is required to have a grounding conductor that goes to a ground rod....

I usually follow your leaps of logic, Bob, but this time, it's a leap of illogic that brought this answer.  The simple act of bonding the copper piping to the house ground puts that piping in 'use' in the ground system.  You simply do not know what that piping connects to or what may be connected to it--intentionally or not.

Perhaps I wasn't clear--I didn't specify the prohibition applies only to completely new construction--but then again most older homes are and were grandfathered in by the simple fact that most of those plumbing systems were completely made of metal, and that those systems were already used as as a part of the grounding system--that must be maintained as installed.

That isn't all, however,  since you seem to contradict your own reply by the statement that "...That prevents the water pipes from every being energized to a different potential than the electrical system ground. The electrical system is required to have a grounding conductor that goes to a ground rod."  Let me specify--if there was that sort of connection and the ground rod or its connection failed, that may well put a lethal charge on the ungrounded water system!

I think you'll agree that picking at nits can sometimes blow up in your face, can't they?  73!
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AA4PB
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« Reply #22 on: April 20, 2013, 11:44:21 AM »

Well, my logic (which I believes conforms to the current code) is that simply bonding the electrical service panel ground buss to a metal water pipe does not ensure that the electrical system is at Earth ground level as required. The water pipes are not "in use" as a the grounding conductor if they have no Earth ground. In the old days it did because the metal water pipe wend outside the house under ground and that provide an Earth ground. The code now requires that you provide an independent grounding conductor from the electrical panel to a ground rod to ensure an Earth ground. In addition in most places you are also required to bond the metal water pipes to that grounding conductor. The purpose for this bond is NOT to provide a ground for the electrical system, but rather to ensure that the metal water pipes are always at the same voltage as the electrical system ground. That's in case someone drops a hair drier or some other electrical device into a sink or bathtub. It won't electrocute someone in another part of the house who is touching both a water pipe and an electrical ground (a microwave case for example).

Lets take my house as an example. I have copper water pipes which are fed by plastic pipe that goes underground to the well. The electrical service panel has a large grounding conductor that goes outside to a ground rod. The panel also has a wire that goes to the water pipe. If I removed the ground rod then there would be no Earth ground on the electrical system or the water pipe. If I removed the bonding wire to the water pipe then there would be nothing to prevent the water pipes from being "energized" to 120V as referenced to the electrical ground pin in each outlet.

So, the NEC does NOT prevent you from connecting metal water pipes to the electrical system ground. What it prevents is you using the water pipes AS the grounding conductor. In fact, most areas REQUIRE you to bond metal water pipes to the electrical panel even though you MUST also have a grounding conductor to a ground rod or other type of Earth ground.

I don't consider it a "nit" because there is a huge difference between saying that the code does not permit you to bond to the water pipe and saying that the code does not permit you to use the water pipe as the grounding conductor or grounding system.
« Last Edit: April 20, 2013, 12:01:49 PM by AA4PB » Logged
AA4PB
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« Reply #23 on: April 20, 2013, 01:05:21 PM »

Lest you think that I'm making this stuff up  Cheesy Here's what the electrical contractor magazine has to say about bonding of water pipe which does NOT have at least 10-feet in direct contact with the Earth:

"Section 250.104(A) requires a metal water piping system installed in or attached to a building to be bonded back to the electrical service. The metal water pipe can be bonded to the electrical service enclosure, the grounded conductor at the service, the grounding electrode conductor where it is of sufficient size, or to one or more of the grounding electrodes for the service.

The main purpose of this bond is to ensure that the metal water pipe is at the same zero voltage to ground as the service grounded conductor. A secondary purpose is to ensure that there is a path back to the service for electrical current flow if the metal water pipe becomes energized."
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K1CJS
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« Reply #24 on: April 21, 2013, 05:38:56 AM »

My simple point is this--and I'll repeat it.  >>You simply do not know what that piping connects to or what may be connected to it--intentionally or not.<<  The simple act of connecting a water pipe/system to a ground point puts the water pipe/system 'in use' as a part of the grounding system because something may already be connected to it, either intentionally or not..

My home was built back in the 1920s, with a water piping system entirely of metal.  It was the grounding system for the electrical panel back then--until the city put in a new water main and replaced the individual feeds with plastic pipe.  Nothing was done to ground the original water system when that was done.  I had to drive a ground rod into the soil at the point that the water main entered the house.  I also ran ground cables and made new connections to both the water piping inside and to the house electrical panel.

Understand that I'm neither condoning or condemning the practice since each house is different in one way or another.   
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AA4PB
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« Reply #25 on: April 21, 2013, 10:49:18 AM »

I *am* condoning bonding a conductive metal water piping system to the electrical system because that is what the National Electric Code requires. You must also have the electrical system connected to an Earth ground rod unless the water system is total metal and has at least 10-feet in direct contact with the Earth. If you do only the latter it is your responsibility to ensure that the piping system meets those requirements. Otherwise you have to add the ground rod.

An electrically "floating" water piping system (i.e. not bonded to the electrical system) can become a shock hazard for residents.


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K1CJS
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« Reply #26 on: April 21, 2013, 11:49:55 AM »

Thank you, brick wall.  Please don't bother me anymore--and I'll return the favor.
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KA4KOE
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« Reply #27 on: April 25, 2013, 03:41:46 PM »

Do not under any circumstances bond the neutral and ground together at the radio. This defeats any action of the circuit breaker in the panel to rapidly clear faults (shorts). Neutral and ground are only permitted to be bonded at your main panel per NFPA 70.

Philip
EE type
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K8AXW
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« Reply #28 on: April 25, 2013, 08:48:17 PM »

CJS: Let me add:  When I bought my new house one of the first things I noticed was the contractor had used the cold water pipe as a panel ground.  From what I understand that was the code back in those days.

After living here for 20+ years I found that the copper water line extended just 12 inches outside the foundation!  From there to the meter was PLASTIC!  So basically, there wasn't a reliable ground on my system at all.

When I had an electrical contractor install a new 200A panel, two ground rods were installed outside as per the new code.
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K1CJS
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« Reply #29 on: April 26, 2013, 04:39:46 AM »

CJS: Let me add:  When I bought my new house one of the first things I noticed was the contractor had used the cold water pipe as a panel ground.  From what I understand that was the code back in those days.

After living here for 20+ years I found that the copper water line extended just 12 inches outside the foundation!  From there to the meter was PLASTIC!  So basically, there wasn't a reliable ground on my system at all.

When I had an electrical contractor install a new 200A panel, two ground rods were installed outside as per the new code.

You would probably be shocked (pun intended) to know how many homes built in the last thirty years were built the same way.  All too many electricians just connect the ground without testing the effectiveness of the individual ground they are 'using'.  The real pity is that it's all too simple to test.

When I did the regrounding at my present home, I was alerted to the fact there was a problem by the cable company.  Yes, the cable company!  It seems that when cable was installed, they just connected to the cold water pipe like the rest of the utility installers do--and the ground was backfeeding through their equipment!  It actually melted the cable drop and damaged associated equipment so that there was a major problem on the cable system centered at my home!

Luckily, I was told I didn't have to pay for the replacement equipment since the original installer should have checked the installation before he left--and he didn't.  I don't think I want to know how much the bill would have been.  
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