CTs have 300V wires, should they be 600V wires?


I had my solar company show up today because there were issues with the wiring being up to NEC code for ground and a number of other things. They also had to replace their CT’s (not Sense) because they had 300v wires to new ones that had 600v wires to bring those up to code.

Looking at Sense CT wires, it states on them 300v.

So my question is, are the Sense CT’s up to NEC or state code (I’m in Massachusetts, same as Sense)?


Odd. Shouldn’t need anywhere near that as the CTs are probably outputting very little voltage/amperage based on current they’re monitoring.

Did solar company have NEC code reference?

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Same question. I tried searching the NEC yesterday, but couldn’t find any requirements - or I wasn’t searching correctly …


The electrician didn’t give me a NEC code, he just had a punch list from inspectors at, I believe, Mass Solar (who oversees installations and credits/rebates in Massachusetts).

But he changed a bare ground to an insulated ground, added a lot more warning stickers and then he changed the CTs for my solar company, Sunpower (not Sense’s solar CT’s) with a new one that he said needed to have 600V rating. I suspect they are worried that a short or melting of the wires could cause more arcing inside panel box.

Of course we all know that the CTs carry almost no amperage or voltage.

But while he left the Sense CTs, he felt they should be upgraded, which is the impetus of this question.


Take a look at this article which may have useful references to the issue
Making Sense of the NEC’s Rules on Industrial Controls


@miracj, Sense’s CT cables are definitely up to NEC/state code. NEC code states that the wires need to be able to handle the maximum amount of voltage (which is 240V in this case).


@BenAtSense Thanks for the info. But there still seems to be a difference between what the electrician said (and he was just following orders of possibly Mass Solar inspectors) and what Sense CT’s had. Clearly, the new CTs he installed for the Solar monitoring were 600V. Perhaps it was for some other reason.

Any chance you can get the applicable NEC code numbers so we can quote it for inspectors in case it comes up for future panel work? Thanks.


@miracj sure! In Article 727.6 of the 2017 edition of the NEC code, it states that “insulation on the conductors shall be rated for 300 volts.” This applies to ‘Instrumentation Tray Cables’, which is what the CT cables are.

Correction: Article 300.3 Section C is the more relevant section.


@BenAtSense Thanks for the info.

But I’m still curious as to why the Solar company felt they needed to change. But alas, we may never know!


I suspect it is because the quoted article applies to Instrumentation Tray installation and your solar install of the CT cable is not an Instrumentation Tray and runs next to AC Mains voltages.


One possibility is the PV panels are connected in series making 600VDC possible. This would be on the DC side of the inverter and if the CTs are in same wiring panel as the PV string then you have more high voltage to consider.


That’s not the case for my solar. It uses microinverters yielding a maximum of 240V AC anywhere off the solar panels.

My guess is that there are two separate interpretations of electrical code, one by Sense and the other by the Mass Solar’s inspectors.


Probably. I read www.reddit.com/r/electricians daily and it feels like they’re always battling inspectors who like to put their own spin on how to interpret NEC.

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