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enter image description hereI added 2 separate circuits to a small space on the first floor.

Both circuits were AFCI/GFI protected in the breaker panel.

Both circuit home runs ran to one junction box before splitting.

1st circuit was 20A single gang outlet, nothing else.

2nd circuit was 15A for direct wired radiant heater (line thermostat controlled) that would draw max 6A.

All grounds were connected in the junction box.

After consultation with the heater/thermostat company I learned that AFCI/GFI breaker cannot be used with the thermostat. It requires a conventional breaker. Conventional 15A breaker installed for the 2nd circuit.

Problem

circuit 1 trips immediately when circuit 2 breaker is switched on.

Circuit 1 does not trip with circuit 2 breaker off and vice versa. (Btw before switching from AFCI to conventional style 2nd breaker only worked if 1st breaker off and vice versa)

Heater (2nd circuit) works fine as long as other breaker is off.

Outlet (1st circuit) works fine as long as other breaker is off.

Eaton breaker panel and Eaton br115 and Eaton All-in-one 20A breakers.

I’m open to all suggestions to resolve.

Thanks very much

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    Can you take a picture of the wiring in the junction box where they split? – Moshe Katz Nov 17 '20 at 23:50
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    Smells like crossed neutrals or a neutral to ground short, but more like crossed neutrals. – Ecnerwal Nov 18 '20 at 0:45
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    > All grounds are connected in the junction box You didn't mention neutrals. What about those? – Harper - Reinstate Monica Nov 18 '20 at 1:42
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    Does this answer your question? Upgrading 2 breakers to AFCI, always trips – Peter Duniho Nov 18 '20 at 3:53
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    You guys are the frickin greatest..... No crossed neutrals in the Jxn box but...... what about in the Breaker panel. Aha 😤 Problem solved. I feel shame and sadness. Try to be sooooo careful and still muck things up. – Handydoc Nov 18 '20 at 16:53
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Neutrals were crossed in the breaker panel. AFCI is happy now.

Many many thanks 🙏 to everyone who took a few seconds from their busy day to help me.

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  • Glad you were able to lick it! – ThreePhaseEel Nov 19 '20 at 0:23

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