ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

Topic Options
Rate This Topic
#211863 - 11/18/13 02:37 PM Class 2 circuit ground
Steve T Offline
Member
Registered: 02/14/01
Posts: 306
Loc: Oak Park, IL, USA
I am looking at a wiring schematic for a control system for a residential HVAC system. There are two different designs, the second stating it is for upgrading from single to two stage air conditioning. This second design shows what I'll presume to be a Class 2 transformer (among other devices), with one line of the load side noted to 'Connect Common to electrical ground', and a standard line drawn with ground symbol at end. Where can this electrical ground occur? Thanks.
Top
2017 / 2014 NEC & Related Books and Study Guides
#211865 - 11/18/13 03:29 PM Re: Class 2 circuit ground [Re: Steve T]
Tesla Offline
Member
Registered: 06/16/04
Posts: 1273
Loc: Sacramento, CA
Load side to ground?

Something's wrong.

Please upload the instructions.

_________________________
Tesla
Top
#211867 - 11/18/13 04:05 PM Re: Class 2 circuit ground [Re: Steve T]
Steve T Offline
Member
Registered: 02/14/01
Posts: 306
Loc: Oak Park, IL, USA
I sent it to the 'Photos@ECN' email. Is there an easier way?
Top
#211968 - 11/25/13 02:54 PM Re: Class 2 circuit ground [Re: Steve T]
Steve T Offline
Member
Registered: 02/14/01
Posts: 306
Loc: Oak Park, IL, USA
Thanks for the instructions Trumpy. I can't reduce a scan to smaller than 100KB to attach.

http://www.fast-stat.net/images/pdf/Model%203000%20Installation%20Instructions%20Set.pdf

See installation Guide B-- "...Grounded Commons Wiring Method..."
Top
#211969 - 11/25/13 04:22 PM Re: Class 2 circuit ground [Re: Steve T]
Tesla Offline
Member
Registered: 06/16/04
Posts: 1273
Loc: Sacramento, CA
Dinky 24VAC 1-phase control transformers are typically fed 120VAC -- regular way.

On their (typically unfused) secondary side one wire is normally 'anchored' to ground whenever a floating neutral must be shunned. (It's not at all unusual for these circuits to 'float' -- not being grounded at all. Think sprinkler controls, door bells, etc.)

The other lead will then become the 24VAC 'hot.'

The pigtail implied in Section B can be landed upon any chassis that is also bonded back to the panel. The amount of current is tiny -- and at a very low voltage, too.

The gadget (Nordic Electronics Fast Stat) is plainly designed to get around old work limitations -- particularly those homes that started life with mere two wire control connections from the thermostat to the furnace.

So one drops in what is best described as a digital multi-plexer and de-multi-plexer pairing. As is typical in digital systems, a floating neutral/ground basis is undesirable, hence the grounding pigtail.



_________________________
Tesla
Top

Member Spotlight
Member Since: 08/22/05
Posts: 44
New in the Gallery:
SE cable question
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box


Who's Online
0 registered (), 56 Guests and 8 Spiders online.
Key: Admin, Global Mod, Mod
 
New in the Gallery:
SE cable question
 
Top Posters (30 Days)
Admin 47
HotLine1 43
gfretwell 19
Ruben Rocha 12
Trumpy 9
 
Newest Members
Stack, Scotto, Freecrowder, clee512, Jdscott2005

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals