historic panel question

[jon_harvey]

Existing 1978 CTL Cutler Hammer panelboard in a residence. Loaded with with layout as follows (the 90 and 60 DP feed Square D load centers)
Left :: RIGHT
90 DP::30 DP
50 DP::30 DP
60 DP::60 DP
15 SP::20 SP
15 SP::20 SP
15 SP::20 SP
15 SP::20 SP
15 SP::20 SP
20 SP::15 GFI SP
20 SP::15 SP

Owner intends to install a 12kW photovoltaic installation adding another 30 years to the 1978 equipment taking service life to 73 years.... We suggest leave existing panel alone, tap the service line, add a new panelboard dedicated for PV installation. As options exist however, would intended panelboard device reliability best be served to also upgrade this panel to a contemporary unit as well?

 

[tortuga]

Did someone say history?
Evaluating an old service panel has many considerations for example
the panel condition,
calculated load,
fault current,
buss bar rating,
main breaker(s) size, older panels can be 'split buss' or even 'tri-buss'

A panel-board may have a very long service life, breakers less so.

 

[jon_harvey]

Concur, general inspection of panel shows no signs of water, thermal abuse, smoke, fire etc. IR survey looks nominal, terminations appear to be tight, logical wire management adequate, understand from other posts on this that the buss bar is likely ~225A.
I took a look at the residence utility bill it indicates 930kWh low-point to 1650 kWh high-point per month in Winter.
Using a 30 day month thus we calculate a profile of 930/30 days = 31 kWh or 129 A loading, and 1650 kWh / 30 days = 55 kWh or 229A loading. Goal for continued safety at breakers end of life behavior by retaining the thermally driven characteristics of a bimetalic strip that bends at an angle releasing the spring loaded trip mechanism. Unknown is the retention of this behavior over ~70 years as I have limited insight into design lifecycle of these breakers. I do know the bimetallic element that snaps the contacts within a power thermostat for a hot water heater element also using a bimetallic frequently fails, this is the other data point fueling my question. Perhapps a refresh on the breakers makes sense. thanks again for your thoughts

 

[retirede]

I took a look at the residence utility bill it indicates 930kWh low-point to 1650 kWh high-point per month in Winter.
Using a 30 day month thus we calculate a profile of 930/30 days = 31 kWh or 129 A loading, and 1650 kWh / 30 days = 55 kWh or 229A loading.

Those calcs are meaningless. In order for those average daily loads to result in the amp loads you ended up with, those KwH would have to all be consumed in one hour.

 

[jon_harvey]

Retirede - your so correct. My error
240v x~5.5 A = 1320 watts if constantly used over 24 hours/day for 30 days provides ~950kHh/month, and
240v x ~9.55 Amps = 2,292 watts if constantly used 24 hours per day for 30 days provides ~1,650 kWh/month,

Much better - thanks

 

[junkhound]

Existing 1978 =panelboard in a residence. =

FWIW, my ;mother's house was electrified in 1914, no idea if the knife switch/fuse main panel (Squared D) was original or later. It was there in 1940 anyway. Still original fuses, still going strong! No contact heating.

Own house has square D QO breakers/panel. Installed 1972. Have checked CB screws and main terminal torque every decade. 4/0mains are aluminum, all else copper. Zero problems, zero breaker nuisance trips. One 20 A breaker to my electronic shop has tripped over 100 times over the years (due to me shorting something or an equipment short) with no problems. Hope to live another 20 years maybe, same panel will still be there.