-48 V used in telecommunications
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hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
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- EC
Re: -48 V used in telecommunications
Tradition.
Tradition.
Re: -48 V used in telecommunications
Yes, I do know why. There are two reasons:
1. One it goes back to the days Telco's used underground lead sheathed cables. By grounding the positive battery post it keeps the lead sheath from deteriorating by electrolysis.
2. The same reason you earth an AC system to stabilize voltages, minimize stress on cable insulation, discharges static, provides a planned path lightning, etc.
Yes, I do know why. There are two reasons:
1. One it goes back to the days Telco's used underground lead sheathed cables. By grounding the positive battery post it keeps the lead sheath from deteriorating by electrolysis.
2. The same reason you earth an AC system to stabilize voltages, minimize stress on cable insulation, discharges static, provides a planned path lightning, etc.
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Re: -48 V used in telecommunications
Now thats a "tip" on a real "ring" of history.
Now thats a "tip" on a real "ring" of history.
Re: -48 V used in telecommunications
Some older American cars (40-50 Dodge If my memory serves) used to have the battery positive connected to the chassis and switched the negative to power the systems.
I never knew why. They also put left hand threads on the right wheel lugs?
steve
[ November 15, 2003, 09:40 AM: Message edited by: hillbilly ]
Some older American cars (40-50 Dodge If my memory serves) used to have the battery positive connected to the chassis and switched the negative to power the systems.
I never knew why. They also put left hand threads on the right wheel lugs?
steve
[ November 15, 2003, 09:40 AM: Message edited by: hillbilly ]
al hildenbrand
Senior Member
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- Minnesota
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- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: -48 V used in telecommunications
LOL!!
LOL!! 
electricman2
Senior Member
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- North Carolina
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- Retired Electrical Contractor
Re: -48 V used in telecommunications
Steve
Steve
Your memory is good, I once twisted two studs off the right rear wheel of a 1956 Olds before I figured it out.
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Re: -48 V used in telecommunications
Chrysler had left threads on there cars all the way up into the "70s"
Tip, Ring = the two connection points of a 1/4" phone plug simular to the head phone plug we use today. used in the phone industry up into the "60s" most famous was on Rowin & martin's Laugh in with Lily Tomlin as the whacky operator using them.
[ November 15, 2003, 10:36 PM: Message edited by: hurk27 ]
Chrysler had left threads on there cars all the way up into the "70s"
Tip, Ring = the two connection points of a 1/4" phone plug simular to the head phone plug we use today. used in the phone industry up into the "60s" most famous was on Rowin & martin's Laugh in with Lily Tomlin as the whacky operator using them.
[ November 15, 2003, 10:36 PM: Message edited by: hurk27 ]
Re: -48 V used in telecommunications
Thanx for all the info. Now I have a follow up question.
If my power supply has positive grounding and the equipment it supplies is also positive grounded internally, surely there will be current flowing thru the ground as well as thru the positive conductor.
This is certainly an undesirable situation. Does anyone have any experience with a similar situation, and if so how is it dealt with?
Can anyone recommend reference material (web sites, books etc.) about DC power supply systems?
Thanx for all the info. Now I have a follow up question.
If my power supply has positive grounding and the equipment it supplies is also positive grounded internally, surely there will be current flowing thru the ground as well as thru the positive conductor.
This is certainly an undesirable situation. Does anyone have any experience with a similar situation, and if so how is it dealt with?
Can anyone recommend reference material (web sites, books etc.) about DC power supply systems?
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: -48 V used in telecommunications
If my power supply has positive grounding and the equipment it supplies is also positive grounded internally, surely there will be current flowing thru the ground as well as thru the positive conductor.
How is that any different than where the negative is grounded? Makes no difference does it.
If my power supply has positive grounding and the equipment it supplies is also positive grounded internally, surely there will be current flowing thru the ground as well as thru the positive conductor.
How is that any different than where the negative is grounded? Makes no difference does it.
Re: -48 V used in telecommunications
I deal with it every day. The equipment is divided into two distinct categories: Isolated ground planes, and integrated ground planes.
Isolated ground plane equipment has the battery return isolated from the equipment chassis and is intended to be installed in a "single-point isolated ground plane".
Integrated ground plane equipment may or may not have the battery return isolated from the chassis and is intended to be installed in the "integrated ground plane" or multi-point grounded.
It all revolves around a ground bar (MGB) installed inside a "ground window", and how the two ground planes are integrated from a common DC power supply.
Most telephone companies have their own engineering and installation practices for grounding and DC power schemes. They are all based off of Bellcore TR-NWT-000295, which is available from Telcordia for about $300. ANSI also has a document availible for sale and is similar to Bellcore, but not as well written IMO. But they are all proprietarily documents (code word for closely gaurded secret)
If you will send me your e-mail address via PM, I can send you a engineering practice that I wrote for a very large telephone company.
[ November 19, 2003, 01:32 PM: Message edited by: dereckbc ]
I deal with it every day. The equipment is divided into two distinct categories: Isolated ground planes, and integrated ground planes.
Isolated ground plane equipment has the battery return isolated from the equipment chassis and is intended to be installed in a "single-point isolated ground plane".
Integrated ground plane equipment may or may not have the battery return isolated from the chassis and is intended to be installed in the "integrated ground plane" or multi-point grounded.
It all revolves around a ground bar (MGB) installed inside a "ground window", and how the two ground planes are integrated from a common DC power supply.
Most telephone companies have their own engineering and installation practices for grounding and DC power schemes. They are all based off of Bellcore TR-NWT-000295, which is available from Telcordia for about $300. ANSI also has a document availible for sale and is similar to Bellcore, but not as well written IMO. But they are all proprietarily documents (code word for closely gaurded secret)
If you will send me your e-mail address via PM, I can send you a engineering practice that I wrote for a very large telephone company.
[ November 19, 2003, 01:32 PM: Message edited by: dereckbc ]
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