Is a 70 amp main breaker in a 100 amp service panel a safety measure?

[jlack]

If a 100 amp service panel that has the proper wire size to that panel has a 70 amp main breaker in it. Would that in theory be a safety measure? We see this in a condominium unit. Thank you.

 

[infinity]

The only issue is if the unit actually required a 100 amp service at the time of installation. {230.79}

 

[ptonsparky]

I don't see it as a safety issue. Too small, it should trip. Lights going out unexpectedly would be the only thing close to safety. I suspect even with a100 amp service calculation, the 70 would be fine.

 

[Dennis Alwon]

The only issue is if the unit actually required a 100 amp service at the time of installation. {230.79}

If the main panel is fed with 100 amp then the 70 amp is a feeder so 230.79 shouldn't come into play

 

[ptonsparky]

If the main panel is fed with 100 amp then the 70 amp is a feeder so 230.79 shouldn't come into play

'in it' as main or feeder protection is the question. I took it as a 70 vs 100 for the main.

 

[infinity]

If the main panel is fed with 100 amp then the 70 amp is a feeder so 230.79 shouldn't come into play

He said it's a service not a feeder.

 

[wwhitney]

I think the question is "why would someone install 100A service conductors and a service panel with a 100A busbar, and then use a 70A main breaker as the service disconnect?"

For the OP, is there any PV (solar) or ESS (batteries) on that service?

Cheers, Wayne

 

[Dennis Alwon]

Well. obviously, I read it incorrectly.... I made some assumptions.
Imo, the breaker decides the service size so a 70 amp breaker does not meet the standards that Infinity link to in 230.79

 

[jlack]

Thank you all!

 

[James L]

Lots of missing info.

I've wired 3 remodels in a condo building built back in the late-40s or early-50s

8 stories with 4 units on each floor

Some units are fed from 40-amp breakers, and some from 70-amp breakers. Each unit had 8-space MLO panel

From what I can ascertain, the difference is whether or not it had an electric range.

But all the units seem to have been fed with #2 copper, my guess being for voltage drop to the highest floor, and they were all pulled with the same wire.

In one unit, I swapped out the panel because it got a full kitchen remodel and I needed more spaces. I used a 100-amp main breaker panel so they could have a disconnect in the unit.

That's what comes to mind when I read the OP

 

[jaggedben]

I have seen some services like this, but they were old, and did not have 'the proper wire size' for 100A.

I think the 100A minimum was started around 1980. @tortuga has been talking about the 60A services that predated that.