ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
220/230/240V 60Hz Systems
by gfretwell. 09/23/18 02:50 PM
Inspection camera help
by petey_c. 09/22/18 07:52 AM
Motion detectors and dimmers
by gfretwell. 09/20/18 04:02 PM
Extension cords
by annemarie1. 09/20/18 08:54 AM
Acronis Backup 2017
by gfretwell. 09/16/18 12:46 AM
New in the Gallery:
Plug terminals
Housebilding DIY wiring
Who's Online Now
0 registered members (), 4 guests, and 31 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Network meters; network service #180212
08/17/08 10:12 PM
08/17/08 10:12 PM
J
junkcollector  Offline OP
Member
Joined: Apr 2007
Posts: 36
Central MN
I've heard about buildings in heavily loaded downtown areas served with what's called a "network service." To me, I look at this setup as as a system of large vault type transformers installed in the street that are paralleled onto the secondary mains and connected with a special switch called a "network protector." I've seen a special kind of electric meter called a "self contained network meter" and needs a fifth terminal? What is the difference between a 120/208 Y network service and a standard 120/208 Y service? I don't understand why a service like this needs a special meter. Perhaps I've got it confused.

If anyone can explain this to me I'd be most greatful. Thanks.

Work Gear for Electricians and the Trades
Re: Network meters; network service [Re: junkcollector] #180215
08/18/08 11:05 AM
08/18/08 11:05 AM
W
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
You may be encountering different uses of the term 'network service', with entirely different meanings.

I have seen the term used to describe 120/208 'single phase' service, such as might be used for individual residences in an apartment building. Such a service is really two legs of a 208/120 wye, and so at the basic physics level is not really 'single phase'; but is used in the same fashion as a residential single phase service.

As to why two legs of a 120/208 service requires a different meter from a 120/240 service: A standard meter for 120/240 single phase service 'cheats' and is not 'blondel compliant'. The 'blondel theorem' basically says that to correctly meter a three wire service you need to make _two_ voltage measurements (say the two leg-neutral voltages), and _two_ current measurements (say the two 'hot' leg currents). A standard 120/240 meter simply makes one voltage measurement (the leg-leg voltage) and then assumes that the leg-neutral voltage is exactly 1/2 of this value. In other words the meter ignores any phase difference or imbalance.

Because of the phase difference present in a two leg 120/208 service, such a meter would read anywhere up to 14% low, not accurate enough for utility metering.

-Jon

Re: Network meters; network service [Re: winnie] #180218
08/18/08 07:26 PM
08/18/08 07:26 PM
J
junkcollector  Offline OP
Member
Joined: Apr 2007
Posts: 36
Central MN
Thanks for the explanation.cool

Basically what you are saying is that you need a meter with two voltage coils, and have each coil connected between the neutral and each hot leg. I would imagine that the neutral would get connected to the sideways fifth terminal, instead of with a standard 120/240 v where the meter is not connected to the nuetral at all (one voltage coil that gets 240, connected to L1 & L2)

That makes sense. Thanks again.


Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
Grover
Grover
Sebago, ME, USA
Posts: 109
Joined: January 2005
Show All Member Profiles 
Top Posters(30 Days)
Admin 13
Trumpy 11
Popular Topics(Views)
249,406 Are you busy
187,336 Re: Forum
176,672 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.015s Queries: 15 (0.004s) Memory: 0.9526 MB (Peak: 1.0756 MB) Zlib enabled. Server Time: 2018-09-23 20:45:17 UTC