# Hazordous transformer location?



## Pcinspector1 (Jan 17, 2013)

I was told by a former inspector that a transformer cannot be concelled in a wall or a breaker box but can't fine the code to cite. Is this true? What code and section?

IRC or NEC?

pc1


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## Pcinspector1 (Jan 17, 2013)

I found this in the NEC 450.13 (B), Would this be the code to cite for a door bell transformer? (B) would prevent a transformer from being installed inside a wall cavity or breaker box that would have no ventilation in either space.

pc1


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## gfretwell (Jan 17, 2013)

450.13(B) says they must be accessible. If an installer put a doorbell transformer in the KO of a device box and then they rocked over it, the transformer would not be accessible. If there was an access plate that could be removed without damaging the building finish, I think it is compliant as long as the wall space was fire resistant and they provided some kind of ventilation. That is still not your average home.

As for the old transformer in the panelboard enclosure, you have class 2 separation problems. The secondary class 2 wires are not properly separated from line voltage. 725.136


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## raider1 (Jan 24, 2013)

Article 450 does not apply to Class 2 transformers.

A Class 2 transformer (Doorbell transformer) would have to have the 120 volt terminations accessible. Installing a Class 2 transformer in a panelboard is a violation of 725.136. You could install the transformer on the outside of a surface mounted panelboard through a knockout in the panelboard.

Chris


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## Dennis (Jan 24, 2013)

There is an instruction for most doorbell tranies that state not to install in an attic because of the heat however as long as it is properly installed and accessible.  I believe a bell transformer can be installed inside a panel if the wire is allowed in Chapter 3-- you cannot have the thermostat or bell wire in the panel.

Look at 300.3©


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## gfretwell (Jan 24, 2013)

When I look there I see the FPN pointing me to 725.136(A)



> Cables and conductors of Class 2 and Class 3 circuits shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non–power-limited fire alarm circuits, and medium-power network-powered broadband communications circuits unless permitted by 725.136(B) through (I).


I don't see anything in (B)-(I) that seems to apply to a doorbell transformer in a panelboard enclosure unless you provide a barrier.


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## Dennis (Jan 24, 2013)

300.3 states that the conductors of different systems must have the insulation of the highest conductor voltage.  I don't believe doorbell wire is 120V but it may be.  The fact that it is from a transformer means we need to know the class of the trany.  If it is class one then with the proper insulation it could be with the higher voltage cables if the insulation is suitable.

There is nothing in the nec that states a transformer can or can't be in the panel.  IMO, is the trany does not overfill the cross sectional area req.  Look at 312.8


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## Dennis (Jan 24, 2013)

Now if the doorbell trany is class 2 as Chris stated then it cannot occupy the space in the panel based on what was stated in 725.136(A)


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## Dennis (Jan 24, 2013)

I guess my point is if you can find a trany that is not class 2 or 3 then it is possible.  In all likelihood it is a violation


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## globe trekker (Jan 25, 2013)

It seems that there are multiple issues at play here. *(1)* access to the transformer &

conductor connections, *(2)* separation of different type circuits - Class 1 from Class 2

or 3, *(3)* installed in a concealed location, such as within a wall cavity or attics.

Did I miss anything?

Also, "Pcinspector1", ..did you get your answer?

.


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## gfretwell (Jan 26, 2013)

If you are using a class 1 transformer and want to exploit that, you need to use a class 1 wiring method and a class 1 rated doorbell and switch.


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## gfretwell (Jan 26, 2013)

I may be missing something but I can't find a rule in 725 that says those class 2 terminals need to be accessible or that you can't bury the transformer. Granted I didn't look that hard.

This falls into the "really?" category when I would talk to the installer. "Is this really what you call good workmanship"?

At that point I would look for other short cuts that are certainly there.


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