GFCI Class 2

wireday

Senior Member
Is there any GFCI protection on the secondary side of a 24 volt wall plugin transformer plugged into a GFCI receptacle? In areas adjacent to kitchen sink/bath areas.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
No.
The secondary of the power supply is not permitted to be grounded so GFCI protection would be useless.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
No.
The secondary of the power supply is not permitted to be grounded so GFCI protection would be useless.
Other than the physical issue of making a grounding connection to a wall wart power supply, what, in general, would prohibit the secondary from being a grounded system?
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
Other than the physical issue of making a grounding connection to a wall wart power supply, what, in general, would prohibit the secondary from being a grounded system?
My reply was based on this:
411.6 Secondary Circuits.
(A) Grounding. Secondary circuits shall not be grounded.
 

morepower

Member
OK, I need some help. I’m looking at several fountains that have 24v ac lights and they are fed through a 120/24v transformer. They are connected to a 50 amp c/b. If I understand the NEC correctly, these lights require gfci protection. I cannot find 12v gfci’s. Any suggestions? There has been an electrocution on this project, prior to me being called in, so I am very cautious.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
GFCIs are required now (2017 code) for all pool circuits that exceed the "low-voltage contact limit", which is defined in 680.2 as 15VAC RMS (21.5V for non-sinusoidal AC, i.e. PWM power supplies). So yes, you need one.

But you would put the GFCI on the 120V circuit FEEDING the transformer, not on the 24V side of the circuit.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Engineer
But you would put the GFCI on the 120V circuit FEEDING the transformer, not on the 24V side of the circuit.
A ground fault on the secondary side of an isolation transformer is not seen as a ground fault by a primary side device.
To be compliant you need GFCI on the secondary side.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
As discussed in morepower's thread on this topic, the GFCI _sensor_ needs to be measuring the secondary side of the isolation transformer, for exactly the reason jim dungar expresses. However the GFCI could interrupt the primary side circuit to remove the hazard.

-Jon
 

GoldDigger

Moderator
Staff member
A ground fault on the secondary side of an isolation transformer is not seen as a ground fault by a primary side device.
To be compliant you need GFCI on the secondary side.
The GFCI on the primary side protects against an insulation fault in the transformer energizing the secondary with line voltage.

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GoldDigger

Moderator
Staff member
That would require one side of the secondary side to be grounded, now wouldn't it.

-Hal
No.
Imagine a short from the high side of the primary to any part of the secondary.
At that point it is reasonable that the insulation within the load on the secondary would break down, and you would have current flowing through water, swimmers, and other paths to ground.
This would produce a shock hazard until the primary GFCI trips.

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