New one for me

found this inside a wall.
can the transformer be covered?


I may be wrong but why not?

Although it looks like warmest spot in your photo, it is not really running that hot. I don’t think there is any actual rule against it… have to think a while… but can not recall any.

Only issue would be heat… and from what you show that appears to not be a serious issue. Did you just take plate off before measurement, so it did not have any time to cool. Just wondering.

I am not concerned about the quantitative measurement (because I am not conducting this service). If I was, I would have made a lot of adjustments to get the right temperature. With the cover on, the heat buildup is the main concern, and I have never seen a transformer covered like this.

The line and low voltage should not be in the same box. The transformer is also not mounted correctly.

This was done a lot here in Cali around 2000 to 2005. It was typically done to house the door bell transformer and at the time was not a violation of the NEC.

What year was the house built?

The prohibition against line and low voltage in the same box has been a code requirement for as long as I know. It definitely pre-dates 2000.

built 1962 remodeled two years ago

They are designed to be mounted outside the box in the air .
Those inside main panels are also wrong .

The line and lv in same box is true, not allowed. I was thinking of xfmr in box… and can not think of any reason why not. In fact for lv remote control lighting there were often box mounted… all be it in larger enclosures. And enclosure were designed for xfmr mounting.

It was around in the 1970s.

Nec450.13. My understanding is that a transformer cannot be buried and require accessibility and ventilation. This may help you for reference.

It does require adequate ventilation, but does not mean it can not be enclosed. There were enclosures built specifically for some transformers. Typically because of cost, doorbell transformers are hung on side of box, with lv outside of box. For a doorbell operation the purchase of a proper enclosure is too high for what it gains, and the lv side needs no protection.

The article you point out is related to all transformers - of any size. However read section B. (also low voltage remote control and door bell transformers were treated differently due to very low secondary voltages and ability to expose their connectors to environments not protected by enclosures)

450.13 Accessibility. All transformers and transformer vaults shall be readily accessible to qualified personnel for inspection and maintenance or shall meet the requirements of 450.13(A) or 450.13(B).

(A) Open Installations. Dry-type transformers 600 volts, nominal, or less, located in the open on walls, columns, or structures, shall not be required to be readily accessible.

(B) Hollow Space Installations. Dry-type transformers 600 volts, nominal, or less and not exceeding 50 kVA shall be permitted in hollow spaces of buildings not permanently closed in by structure, provided they meet the ventilation requirements of 450.9 and separation from combustible materials requirements of 450.21(A). Transformers so installed shall not be required to be readily accessible.

Having said that the two voltages can not be mixed in same enclosure.

It’s real simlpe guys.

Mixing low voltage and line voltage in the same box or raceway is not permitted.

You are one faut away from having 120volts appear on the low voltage wiring.

Don’t do it.

Inform, recommend, let the buyer decide. Move on.

See NEC 725.55(D) if you happen to have the 1999 code book lying around…
Also see

Thanks for input!

Be careful in your *interpretation *of Carte blanche acceptance of high/low voltage in the same box issue; such as high-voltage will get onto the low voltage due to a fault.

For the most part you do not mix high and low but there is a lot of equipment panels that have high and low voltage in the same panel.

Low voltage exterior lighting
Irrigation sprinkler systems

Be sure to refer to the equipment manufacturer concerning installation.

As for the original OP; concerning heat.

#1 was the box covered?

#2 101° temperature does not exceed wiring insulation capacity.

Reference: “how hot is too hot” concerning infrared thermal imaging practices. If your going to use infrared thermal imaging to find heated electrical circuits you must be fully aware of this criteria.

The insulation rating for most low voltage is not adequate for use in higher voltage environment.

And equipment cabinet is not a junction box or raceway.

The appliance is tested and the insulation values of all wiring must meet the standard it is evaluated too not necessarily the NEC.

It’s an apples and Oranges thing.