Thermometer Mandatory or Not?

What does the specification say?

What does the transformer manufacturer say, given the ambient temperature (which isn't stated in the original post)? How did the phone call go?

Thermometer or over temperature trip? I wouldn't say mandatory, but I would say advisable.

As PWS has said, speak to the transformer manufacturer.

I've fitted quite a number of distribution transformers, some had O/T trips, and some didn't. It depended on what was specified for the location.

A thermometer would be good for reading the oil temperature.

An over-temp trip would be good for saving the transformer.

But, see #1 and #2 above, They're the experts. I'm just a troll.

On such a small unit, many times they do not have a thermometer (AL) or trip (ALR). Since it is oil filled it is most likely a 55/65 (degree Celsius rise over ambient)Ambient is normally 30/40 Cesius, so you are looking at a maximum of 105 Celcius. Alarm is frequently set at 105 with a trip at 120 Celcuis. Note that this is average top oil temperature and the hot spot is even higher. The nameplate should give the temperature rating. If it doesn't have a device, just use a point and shoot IR probe, they can be purchased for less than $20 and are fast and just as good as a gauge. The temperature can seem really hot and can cause a burn on touch. If you can hold your hand on the unit indefinitely at the area of the top of the oil on the tank which is well below the top of the transformer you do not have a problem.