Today Reuben and Tessa talk about how to determine the electrical service size at a home, mostly related to inspecting the main panel.
Reuben explains that new construction homes use 150 to 200 amps service size panels, and which service sizes are no longer acceptable today. Tessa highlights the different things that home inspectors need to determine: the service size, what the panel is rated for, and how much amperage is coming through the panel.
They talk about how to identify the size of the service panel with the shape of the meter base. They also talk about the strange locations of electrical panels such as in the basement and in the alley. They also talk about the sizes of wires for copper and aluminum. Lastly, they discuss the over-current protection device.
Visit Reuben’s blog post about electrical panels: https://structuretech.com/old-fuse-panel-60-amps-or-100-amps.
The following is a transcription from an audio recording. Although the transcription is largely accurate, in some cases it may be slightly incomplete or contain minor inaccuracies due to inaudible passages or transcription errors.
Reuben Saltzman: Welcome to my house. Welcome to the Structure Talk podcast, a production of Structure Tech Home Inspections. My name is Reuben Saltzman. I’m your host alongside building science geek Tessa Murray. We help home inspectors up their game through education, and we help homeowners to be better stewards of their houses. We’ve been keeping it real on this podcast since 2019, and we are also the number one home inspection podcast in the world, according to my mom.
RS: All right, Tess. So this week we’re kind of tying this in to the blog again, and we’re gonna do a fairly short episode here because it’s a fairly simple topic, but we’re gonna talk a little bit about inspecting old fuse panels. This is a very specific topic. You have taught a lot of inspectors on our team how to inspect electrical panels, fuse panels, the difference between 60 and a 100 amp and split bus panel. So we’re gonna talk about all that stuff today.
Tessa Murray: Yeah, I feel like it’s a topic that’s a little intimidating for most people at least. Well, maybe that’s just me. Electrical is an intimidating topic to me, I think. And even though yes, I have taught a lot of our inspectors on the team and people we’ve hired and stuff how to inspect them, I still feel like it’s something I am always learning about. And even just reading through your recent blog on them, I feel like I picked up a couple things too.
RS: Oh, good. Good. Yeah, it never ends with electrical. I feel like no matter how much you think you know, there’s gonna be somebody behind you that’s gonna make you look stupid ’cause they know so much more than you. Yeah.
TM: Yes. Yeah. Yes. Yeah. Yeah. It was always one of those things when I was inspecting, I always had questions about electrical things and I luckily I would text you or someone else on the team who was way more experienced than me and we could figure out an answer. But it’s a lot of times it’s not cut and dry either. It’s not necessarily something that you can say, yeah, that’s a 100% wrong. Sometimes there’s variables that make it challenging.
RS: Well, and that’s what brings up today’s topic. There’s an inspector on our team who had shared on our internal discussion board, he had shared a bunch of photos of an electrical panel at his inspection. He was saying, “Guys, what am I looking at here? Is this a 60 amp panel or a 100 amp panel?” And he took very good photos. He’s got photos of the outside of the panel and the inside and the labels and the meter and everything. And after looking at all of it, I couldn’t figure it out. We could not give him a definitive answer, but.
TM: That makes me feel better that you couldn’t figure it out by looking at it. Okay.
RS: Yeah, but I did write a blog post about it to just discuss all of this because I wanted to lay out all of the stuff that we do think about when we’re trying to figure out the size of the panel. And I could tell them with about 99% certainty that this tiny little fuse panel he was looking at was a 100 amp panel. But I couldn’t find anything that definitively said it on there. And that’s probably one of the most important things that we look for is just a label that says what the panel’s rated at. We’ll have a couple of photos in our show notes, but in one of these photos, there’s a label on this tiny little fuse panel. It says very clearly 100 amps. So there, you’ve got a 100 amp panel. Now is it a 100 amp service? Because a 100 amp service is not the same thing as a 100 amp panel.
TM: Oh my gosh. Okay. Well, before we dive into that more,’cause I do wanna hear some more detailed conversation on this and your thought process too for the things that you look at to determine service size and everything, let’s just back up for a second and why is it a big deal that we’re even talking about like a 60 amp service versus a 100 amp service? Like what do most houses have for a service size? What do we typically see?
RS: Well, new construction today, I’d say it’s pretty much all 150 to 200 amps. I mean, 200 amps is pretty standard. They just put in big service and they say you got plenty of room for expansion and we never need to worry about it. But the minimum size you can put in today is 100 amps. You can get a surprising amount of coverage with a 100 amp service. I know when I used to… When I was taking these electrical inspection classes, we had to do these load calcs and I did a load calc at my own house to figure out what I needed. And at the time, I had a one and a half story house in Minneapolis. I only had one major 240 volt appliance. It was the air conditioner and you add up everything and I needed like 50.9 amps at my house. So my 100 amp service was nearly twice what I really needed. But it was still the minimal allowable.
TM: Yeah. So 60 amps is a big deal because it’s not even allowed for modern houses today. They need a bigger service fuse.
RS: Yeah, yeah. You wouldn’t put in a 60 amp service today. And not only that, but a lot of insurance companies get kinda whipped up when there’s a 60 amp service. I think they get more whipped up about fuse services, but a lot of them just don’t like to see a 60 amp service. Either they’re gonna charge more for insurance or they’re not going to insure the home if you have a service size of 60 amps and…
RS: And it’s one of those things that as home inspectors we need to report on the service size. Our standard of practice says we need to describe what the service size is. And, again, service size is the service size. That’s the total that the house can use coming in. It’s not the same thing as the electrical panel size. You could have a panel that’s rated for 200 amps and you could have a 60 amp breaker in there and no more than 60 is gonna come in. It could be a 60 amp service, yet you have a 200 amp panel and that’s not a defect. It probably is a defect. There’s probably gonna be something wrong if we see that. If we see a 60 amps service and there’s a 200 amps panel, there was probably somebody messing around in there without a permit. That’s usually the case, but not 100%, only probably. Does that make sense?
TM: Okay yeah, it does. Service size coming in does not always match what the panel can handle.
RS: That’s right.
TM: So there’s a lot of different things that we look at as a home inspector to try and determine, okay, well first of all, what is the service size? And then what is your panel rated for? And how much amperage do you have coming through the panel in the house?
RS: Yeah. I don’t think I’m exaggerating here though, when I say probably 99% of the time, the two are the same. It’s pretty unusual to find panel size that doesn’t match the service size. So almost every time, if you see a 100 amps panel, it’s gonna be a 100 amps service, just not 100% of the time.
TM: Yeah, okay, right. So this is probably something though, this 1% is probably something you’d find in an older house, right?
RS: Yes, yes, exactly. Yeah. And then another clue that points you in the direction of what the service size is is gonna be the size and shape of the meter on the outside of the house or the meter base. You know about all those, right?
TM: Yeah. Yeah. So a lot of houses, if it’s like an overhead service, you can trace those main wires to your house and then follow the mask down along the outside wall and it’ll come to the actual meter box itself, that’s what you’re talking about?
RS: Yeah, exactly. Yeah.
TM: The box that holds the meter. Yep. And so there’s a clue there you’re saying that indicates the service size?
RS: Yeah, if it’s a round meter base, where the base is it’s round. We’ll leave it at that. It’s almost always 60 amps. Now, according to Douglas Hansen, code guru Douglas Hansen, that doesn’t mean that it has to be 60 amps. You can still have a 100 amps service with a round meter base. So don’t take that round meter base as gospel. Don’t take it as a rule that this is 60 amps. It’s just probably 60 amps. And then if you’ve got a square meter base, it’s almost always 100 amps. And then when you start getting into a rectangular meter base, it’s probably gonna be 150 amps or more. Now, not always. I had a really unusual situation when I lived in Minneapolis, where I had this huge rectangular meter base, but I only had a 100 amps service, but it was also really weird where my meter was located on the power pole. I want you to think that through. So you had a service drop. The service drop came down from the overhead wires in the alley. They came down on this conduit, and my meter was attached to the power pole, and then the wires went back up the conduit, out of the meter, up the power pole, and then into my house and I had no meter attached to my house, the meter was in the alley.
TM: No, that’s so, I’ve never seen that before.
RS: It’s the only house I’ve ever seen it on myself. Yeah.
TM: I wonder why.
RS: All I know is the rumors that I heard about the previous owner from all my neighbors, and apparently the person who used to live there really did not like people coming on his property, very private. And I think he was able to pull some strings somehow to make it so that nobody would’ve to enter his property to take meter readings.
TM: Wow, okay.
RS: But I don’t know, I don’t know.
TM: Yeah, that’s a very unique circumstance. And actually, I’ve seen meters in basements before too, have you come across that?
RS: Yeah, that’s unusual and if you see a meter in a basement, I have never seen a meter in a basement with a 100 amps service, it’s either going to be a 30 amps service. Yeah, you heard me right. 30 amps service or 60 amps service. One of those two. Yeah.
TM: Okay, so that’s another indicator. If you see the meter in kind of a strange location, either a round socket or a round metal box or in a different location.
RS: Yeah. It’ll point you in that direction. And then another limiter is the size of the wires coming in known as the service entrance conductors or SECs…
TM: Coming into the panel?
RS: Coming into the panel, exactly.
TM: You’re talking about?
RS: Now over…
TM: So you’ll need to remove the cover in order to inspect that part of it?
TM: A normal, yeah. It’s just, if you’re looking at the panel with the door open, you won’t see it. You have to take the cover off.
TM: That’s right. That’s right. We gotta inspect the interior of the panel. And we’re not talking about the overhead wires. Those are owned by the utility company. They can do whatever they want. We don’t concern ourselves with the size of those overhead wires. It’s just the size of the wires coming into the panel. Those are the service entrance conductors. And for… Well, I’m not gonna get in at all the wire sizes. Look at a chart, and there’s different wire sizes for copper and aluminum. The aluminum wires are always gonna be one size bigger, but good rule of thumb there, just one size we’ll talk about. If it’s number four copper or number two aluminum, that’s good for 100 amps. And as a home inspector, you start to get familiar with all these different wire sizes, and you’re usually able to tell at a glance, okay, does this look too big? Is this… Does this look too small?
TM: Too small.
RS: Is what I meant to say. There’s never too big. You can always go bigger.
TM: Yeah. And explain that. Why would it be a problem if the wire’s too small?
RS: Too small, it’s not going to handle sufficient current, and it could overheat and could start on fire. That’s the bottom line.
TM: So if you’ve got a wire that’s rated for 60 amps and it comes into a panel and the main breaker is 100 amps, that wire can overheat and the breaker’s not gonna trip?
RS: That’s right, exactly.
TM: And it can start a fire. Okay.
RS: Now, we’d look at the meter base. We’d look at the wire sizes. We’d look at the panel size, and then of course, the final thing we look at is the over current protection device, which is a fancy way of saying fuse or circuit breaker. What’s the main fuse or what’s the main circuit breaker? And on most panels, it’s just gonna be one. You have a big breaker that’s labeled 100 amps, or you have a single fuse block where you pull out the fuses and inside you’ve got, say, 60 amps fuses or 100 amps fuses, and that gives away the service size right there. But I say most because somewhere between, what was it? I think it’s like 1965 to 1981. I’ll have to check my facts. If I’m wrong, I’ll have to come back and edit this podcast.
RS: But somewhere in that time, we were allowed to have something called the split bus panel, where it would be more than one hand movement to shut off all the power, more than just one circuit breaker. So you were allowed to have up to six of them to shut off all the power inside of one panel. So you could have a breaker that shuts off power to the dryer, one that shuts up power to the water heater, one for the air conditioner, and then maybe another breaker that shuts off power to the bottom half of the panel. And so that’s why they would call this a split bus panel where it’s split up into two different distribution systems for the power.
TM: So what did this panel look like that had the home inspector stumped? Was it a fuse panel or was it a breaker panel?
RS: It was a fuse panel and it had two fuse block pull-outs at the top, and then it had four screw-in glass fuses down below that, really small panels.
TM: Huh, okay.
RS: So really small panels. So you got four 120-volt circuits, and then you got one pull-out that shuts off all the power to those below, and then one more fuse for a 240-volt circuit and one more fused pull-out for a 240. That’s it, that’s all. This is a tiny little panel. And so usually when you see a panel that size, you just assume, okay, it’s gotta be a 60 amp service, but we looked at this more closely, and I don’t think we could actually figure this out for this panel, but a lot of those old fuse panels are gonna be a split bus fuse panel. Oh wait, we did figure it out on this one because both of these fuse block pull outs said Main, indicating the way to shut off all the power is to pull out both of those fuse blocks.
TM: Both, okay.
RS: Yes, yes. And that tells us this is a split bus panel. And on those split bus panels usually the way it worked is you’d have a 60 amp fuse block, so you pull out those 60 amp fuses and you’re disconnecting power to those four screw-in fuses below, but you’re not disconnecting power to the other fuse block. That other fuse block gets its own power directly from the wires coming in, and those are gonna send out power to a 240-volt appliance, so you gotta pull out both of those to shut off all the power. I would bet any sum of money that this is a 100 amp panel.
TM: Yeah, I was gonna say that’s tough because when you’re inspecting, we don’t pull those fuse blocks out…
TM: Typically when we’re inspecting ’cause it’s gonna kill the power to the house.
TM: So we’re just looking at it and if it doesn’t have Main labeled on it, we’re not able to determine what it’s going to or how it’s working, or even what the amperage is of those fuse blocks to be able to determine if it’s 60, or 10, or 50, or whatever.
RS: Exactly. Yeah. Unless there’s a label, there usually is a label, but in this case the label was illegible. It was totally faded and scraped off, couldn’t figure anything out.
TM: Yeah. And you’re talking about the label, the piece of paper that’s usually on the inside of the panel door when you open it.
RS: That’s right. Exactly.
TM: It’ll say it right there what it’s rated for. Another thing too, I think a lot of people wonder about, is there anything inherently dangerous about having a fuse panel itself compared to circuit breaker panel?
RS: No. Fuses are perfectly safe. Nothing wrong with them. Once they blow, they have blown. Now, insurance companies don’t like them because they’re old, they’re outdated, it means that you’ve got an old electrical system, it’s easy to overload stuff, and fuse panels can be tampered with. With a bunch of those old Edison-base fuses, and they call them the Edison-base fuse or fused-based, because you could take a light bulb and actually screw it into that fuse base, it was the exact same threads. So you can get, say, it’s a 15 amp circuit and it keeps blowing, well, you get annoyed that it keeps blowing and so you just get a 30 amp fuse instead and you screw it in there. So it was a lot easier to tamper with fuse services. Doesn’t mean fuses are at all unsafe, just means that…
TM: Right. It’s when people mess with it. When the homeowner puts a copper penny in there or a larger fuse so that it doesn’t blow that’s when we’re potentially creating fires. That’s the problem.
RS: Yeah. Exactly.
TM: Okay. So to summarize, Reuben, it sounds like there’s a few check points you have mentally when you’re trying to assess a situation where you’re not exactly sure what the panel size is, right?
RS: Yeah. Well, service size. When we’re not sure about the service.
TM: Service size, okay. Service.
RS: We’ll try to figure out the panel size, we’ll look at the service entrance conductors, we’ll look at the meter, and we’ll look at the maximum over-current protection device. And of course as part of doing that, we need to figure out is this a split bus panel, is there more than one over a current protection device inside of that one panel enclosure? Those are the four things we look at to help determine the service size.
TM: Yeah. And it’s really easy when there is an actual label you can read on the inside of the panel. When it’s not there, then you’re trying to figure it out with these other methods.
RS: Exactly. And even if the panel size is labeled, it’s not synonymous with the service size 100% of the time. Most of the time it is, but we can’t just hang our hat on that. We gotta look at everything.
TM: Well, these are some really good tips, and if you’re a home inspector inspecting some older houses out there that might have older panels or fuse panels, hopefully this is helpful to you. Or even if you’re a homeowner and you’re trying to figure out your own panel and you’ve got one of these, hopefully this has been helpful to you.
RS: I hope so. Probably lost a lot of people to this one but you know what, too bad.
TM: It was a pretty technical… This was a pretty technical one today.
RS: And you know what, we said at the beginning of the year, we’re gonna get really specific with a few of these. That’s okay.
TM: Yes. Yes we did. We gave you a fair warning, poor listeners.
RS: Alright. Tessa, thank you for being my co-host. Sure appreciate it.
TM: Hey, it’s been fun.