Yea that’s basically what we told the client that the panel was going to need to be replaced anyway
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So how would you determine the service size?
The service “size” is determined by the breaker. The components would determine if it was sized correctly. Wire can be oversized, or breakers undersized. If there is no clear rating then, imho, is should be noted as such.
If you feel inclined to indicate the wire size and ampacity that great but you “can” attach a 200a wire to a 100a bus. Also temp rating of termination and insulation type can change the ampacity of the conductor. The nec is a large complicated book and I would always advise caution to anyone who may or may not understand it in detail. I’ve been reading it for 12 straight years and I’ll still get corrected every once in a while.
Here we go again 
My guess is that it is a 125 AMP service with a possible 150 AMP load.
Did I miss something? Have I given bad info?
FYI - if anyone is guessing what the service size is here is what electricians used prior to the 2014 NEC.
Theres multiple main breakers on the split bus so it cant be determined off of it. All the top breakers are mains up to 6
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Right, so technically you have 2-30’s, 1-40 and a 50a
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Yep so the only real way with these is either to look at the service size or what’s labeled on the inside panel sticker. This service didnt have markings on it so it was down to the sticker. I’m still not good at sizing up larger wires by eye.
Service rating: service panel is fp split-phase type with 4 main breakers. 30,30,40,50. Fp panels are known to be unsafe due to falsifying tests on their products. Defect, safety issue etc. contact electrician immediately for replacement.
That’s basically all that I would say
Yea the federal Pacific is the main concern but for some reason the buyer was concerned with the amperage.
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This might get us through the holidays… 
Yea I get it. Especially in a service industry you want to please the customer too. If the service is overhead and you can see the wire size into the meter then into the panel and your confident. Go ahead and speculate.
If it’s underground and can’t see the utility wires entering the the meter, I would not answer that question with my head in a vice. Hahaha.
It’s # 2 copper wire. #2 copper THHN witch is the modern equivalent would be 150 amps. That being said you would need to go by the manufacture label on the panel to determine service size. If gone I would use the exterior meter socket to determine service size. If it is a 100 amp meter socket then the service size is 100 amps. If it’s a 200 amp meter socket then the service would of been 150 amps.
If the meter socket is 100 amps and the conductors are at least 100 amps why would that be incorrect?
Yes exercise me 125 amps if it’s a 200 amp meter socket
That’s correct. One other thing to note is the insulation type. A 40-50 year old service might have type TW insulation which was not permitted in older editions of the NEC to use the reduced conductor size table for dwelling services.