{"id":3585,"date":"2026-10-08T09:43:15","date_gmt":"2026-10-08T01:43:15","guid":{"rendered":"http:\/\/www.peglersdesigns.com\/blog\/?p=3585"},"modified":"2026-10-08T09:43:15","modified_gmt":"2026-10-08T01:43:15","slug":"can-secondary-circuit-testing-equipment-be-used-for-testing-auxiliary-circuits-in-electr-49aa-30cf9d","status":"publish","type":"post","link":"http:\/\/www.peglersdesigns.com\/blog\/2026\/10\/08\/can-secondary-circuit-testing-equipment-be-used-for-testing-auxiliary-circuits-in-electr-49aa-30cf9d\/","title":{"rendered":"Can secondary circuit testing equipment be used for testing auxiliary circuits in electrical devices?"},"content":{"rendered":"

Hey everyone, let\u2019s cut to the chase because I get this question at least 3 times a week\u2014especially from electricians, maintenance techs, and small engineering shop guys who walk into our workshop or slide into my DMs: \u201cCan the secondary circuit testing equipment you sell actually work for testing auxiliary circuits? Not just the big power stuff.\u201d For a long time, I used to fumble through the answer because I was still wrapping my head around the difference between the two, plus a lot of old heads in the industry swear that \u201caux circuits are just small potatoes\u2014use a multimeter and call it a day.\u201d But here\u2019s the thing: I\u2019ve been selling secondary circuit testing gear for 7 years now, and I\u2019ve seen first-hand how much that mindset costs people\u2014mistakes, downtime, even tiny fires that could\u2019ve been avoided. So let\u2019s break this down like I\u2019m chatting with a buddy who\u2019s knee-deep in a transformer or switchgear right now, no fancy jargon, just real talk. Secondary Circuit Testing Equipment<\/a><\/p>\n

<\/p>\n

First, let\u2019s get the basics straight because people mix these two up all the time\u2014part of why that question is even a thing. Secondary circuits are the low-voltage (usually 120V down to a few volts) control circuits that run show all the bells and whistles on big electrical stuff: the relays that trip when there\u2019s a fault, the voltmeters that tell you how much juice is flowing, the switches that turn on a factory conveyor belt or a building\u2019s HVAC system. Think of them as the brain of your electrical setup\u2014they don\u2019t carry huge power, but they control everything that does. Auxiliary circuits, on the other hand? Yeah, they\u2019re a subset of secondary circuits, but wait\u2014no, hold on, that\u2019s where the confusion hits. Aux circuits are the little extra circuits that run supporting functions for the main secondary or power system: like the 24V supply that powers a relay\u2019s coil, the small circuit that lights up a pilot light on a breaker panel, or the circuit that opens a circuit breaker\u2019s auxiliary contact when the main one trips. So everyone lumps \u201ctesting secondary circuits\u201d and \u201ctesting auxiliary circuits\u201d together, right? But the old guard would say \u201csecondary is for big control relays and trip circuits, aux is just those tiny add-ons, so they\u2019re different.\u201d That\u2019s not wrong, but it\u2019s not the whole story\u2014and that\u2019s where my gear comes in.<\/p>\n

When I first started selling secondary circuit testers, they were big, clunky boxes\u2014think 50 lbs, heavy cords, only made for testing 120V control circuits on 480V switchgear or big transformers. They could send a simulated fault signal to test if a relay would trip correctly, check contact resistance, and do basic continuity. Back then, I\u2019d have to explain to customers: \u201cNah, this is for the big secondary control circuits, not your little aux stuff.\u201d But about 5 years ago, we redesigned the line\u2014smaller, lighter, more flexible models, and that\u2019s when I started realizing the overlap is way bigger than people think. Let\u2019s talk about what both types of testing actually need, because that\u2019s the real backbone of this question.<\/p>\n

What do you need to test a secondary control circuit properly? First, you need to inject a precise voltage or current signal, not just use your multimeter\u2019s built-in leads. Why? Because when a circuit is energized under real load, stray resistance from bad connections or a worn relay contact won\u2019t show up on a multimeter unless you pull it apart. Second, you need to simulate real-world faults\u2014like a short, a drop in voltage, or a delayed signal from a sensor\u2014to make sure the relays and breakers actually trip when they\u2019re supposed to. Third, you need to be able to test over a range of voltages, because secondary circuits can run anywhere from 24V up to 120V, and aux circuits almost always run at the lower end of that range (24V, 48V, 120V).<\/p>\n

Guess what? Most of the mid-tier to advanced secondary circuit testing equipment we sell does all that. Let\u2019s use our best-selling model as an example\u2014let\u2019s call it the CT-12 (I can\u2019t use real company names, but this is the actual model most techs grab). It can output a variable signal from 0V to 150V, inject current up to 10A, and has a built-in continuity tester that doesn\u2019t just blink a light\u2014it measures resistance down to 0.01 ohms. It also has pre-loaded test sequences for common control circuits, but here\u2019s the secret: those sequences are super easy to adjust for aux circuits. Last year, a guy named Jake from a water treatment plant in Ohio called me panicking at 2PM on a Friday. He was supposed to do a yearly test on the auxiliary circuits for their main pump, and his multimeter died. He had a brand new CT-12 we\u2019d sold him 2 months prior, and he texted me a pic of a tiny 24V aux relay coil. \u201cCan I use this to test if this coil will hold a charge when the breaker trips?\u201d he asked. I told him to hook it up to the coil\u2019s terminals, set the voltage to 24V, and run the \u201crelay coil test\u201d sequence. He called me back 10 minutes later\u2014said it worked way better than his old multimeter. The CT-12 didn\u2019t just tell him continuity; it checked that the coil could handle 24V without dropping more than 0.5V across it, which is exactly what an aux circuit needs. A multimeter would\u2019ve just said \u201cgood continuity\u201d even if the coil had a hidden short that would fail when the pump was running.<\/p>\n

But wait, I\u2019m not here to say that secondary testing gear is a one-size-fits-all. Let\u2019s be honest: if you\u2019ve got a tiny, standalone auxiliary circuit\u2014like a 12V pilot light on a residential breaker panel\u2014you don\u2019t need to haul a 15-lb secondary tester out. A $20 multimeter works fine there. But the gray area is where most people get tripped up. For example, if you\u2019re testing the auxiliary circuits on a medium-voltage transformer that feeds a grocery store\u2019s refrigeration system, or the aux circuits on a large HVAC unit for a hospital? That\u2019s when that line between secondary and auxiliary blurs. Those aux circuits aren\u2019t tiny little afterthoughts\u2014they run 24V to power multiple sensors, control the pump motors, and trigger alarms if something goes wrong. Trying to test those with a basic multimeter is like trying to cut a 2×4 with a butter knife\u2014it works in a pinch, but you\u2019ll get a messy cut and maybe hurt yourself.<\/p>\n

Another big point people miss: standard auxiliary circuit testing usually only checks continuity and voltage, but secondary circuit testing equipment does a load test that\u2019s way more accurate. Let\u2019s take contact resistance, which is critical for both. If an aux contact on a breaker has 0.2 ohms of resistance instead of the ideal 0.05 ohms, that might not seem like a big deal\u2014until it\u2019s carrying 5A for 8 hours a day. That extra resistance creates heat, and over time, it can burn through the contact, leading to a partial outage or even a fire. A multimeter can measure that resistance, but it only does it at very low current (like the tiny current it uses for continuity). Secondary circuit testers inject current at the actual load level, so you get a real, accurate reading. That\u2019s not a \u201cnice to have\u201d\u2014that\u2019s the difference between catching a bad contact before it fails and dealing with a 12-hour shutdown at a factory.<\/p>\n

I\u2019ve seen so many horror stories over the years because of this. A manufacturing plant in Michigan hired a third-party tech to test their auxiliary circuits for their assembly line. The tech used a cheap multimeter, found continuity on all the aux relay coils, and called it good. 3 months later, one of the coils had a hidden high-resistance spot, so the relay would only trip at 80% of its rated voltage. When the line was running at full load, the voltage dropped, the relay didn\u2019t trip, and the motor overheated, causing $200k in damage and 2 days of downtime. The plant ended up calling me, and we sent a team out to test all their secondary and auxiliary circuits. We used our CT-15 model, which can handle up to 20A of load, and found 4 other high-resistance aux contacts that the third-party tech missed. That\u2019s when the plant realized: testing aux circuits with the right gear isn\u2019t overkill\u2014it\u2019s just good maintenance.<\/p>\n

Now, let\u2019s address the elephant in the room: why do some people say you shouldn\u2019t use secondary testing equipment for aux circuits? A lot of it is old-school bias. I\u2019ve heard guys say \u201csecondary testers are too big, too expensive\u201d or \u201cthey\u2019re overkill for small aux circuits.\u201d The truth is, a lot of the big, bulky secondary testers from 10 years ago were overkill for small stuff, but the newer models are smaller, lighter, and way more affordable than they used to be. When I started, a basic secondary tester cost around $1,500; now, our entry-level model is under $500, and it still does 90% of the stuff you need for both secondary control and most auxiliary circuits. For the small aux circuits that don\u2019t need it, yeah, use a multimeter\u2014but for any auxiliary circuit that\u2019s tied to a critical system (pumps, HVAC, assembly lines, power grids), the right secondary tester is worth every penny.<\/p>\n

Another myth: secondary testing gear is only for high-voltage stuff. No way. Most of our testers work on low-voltage circuits too, because the core functionality\u2014signal injection, load testing, fault simulation\u2014doesn\u2019t care if you\u2019re dealing with 120V or 24V. You just adjust the settings on the tester. That\u2019s the beauty of it. Let\u2019s say you\u2019re an electrician working on a new office building. You\u2019ve got 24V auxiliary circuits for the fire alarm system, plus 120V secondary control circuits for the elevators. Instead of carrying two different tools (a multimeter, a small aux circuit tester, and a secondary circuit tester), you can just bring one secondary testing unit. It\u2019s one less thing to haul, one less thing to charge, and it gives you consistent, reliable readings across all the circuits you\u2019re testing.<\/p>\n

I also want to talk about ease of use, because that\u2019s a big selling point for our gear. A lot of people think secondary testing equipment is complicated, like you need an engineering degree to run it. But we design all our models with user-friendly interfaces\u2014big, backlit screens, pre-set test modes, and step-by-step guides. Jake, the water treatment plant guy I mentioned earlier, is a maintenance tech, not an engineer. He had never used a secondary circuit tester before, and he got his aux circuit test done in 10 minutes, no training needed. That\u2019s a huge deal for small shops and in-field work, where you don\u2019t have time to sit through a 4-hour training course on a new tool.<\/p>\n

Now, let\u2019s make sure I\u2019m not pitching something that doesn\u2019t exist. Let\u2019s outline the real limits here, because I don\u2019t want to mislead anyone. If you\u2019re testing a tiny, low-current auxiliary circuit\u2014like a 5V LED indicator light on a residential garage door opener\u2014our secondary testing gear is overkill, and a multimeter is better. It\u2019s smaller, cheaper, and does the job just fine. But if you\u2019re testing auxiliary circuits for commercial or industrial systems\u2014anything that\u2019s tied to equipment that\u2019s critical for operations, safety, or power\u2014our secondary circuit testing equipment works perfectly, and in many cases, it\u2019s better than using tools that are only designed for aux circuits. Why? Because those aux circuit-specific tools are usually only made to check continuity and voltage, while our gear does load testing, fault simulation, and resistance measurements at actual operating currents. That\u2019s the difference between passing a test on paper and knowing the circuit will hold up when things get rough.<\/p>\n

I always tell our customers: don\u2019t fall for the \u201ckeep tools in their lane\u201d myth when it comes to electrical testing. The best techs I know are the ones who can adapt their tools to the job, not the other way around. Our secondary circuit testing equipment isn\u2019t just for big power control circuits\u2014it\u2019s a versatile tool that can pull double duty for most auxiliary circuits too. We\u2019ve got customers in everything from food processing plants to wind farms to hospital facilities who use our gear for both secondary control testing and auxiliary circuit testing, and they tell us it\u2019s cut their tool roll weight in half and reduced their testing time by 30%.<\/p>\n

<\/p>\n

If you\u2019re someone who\u2019s dealing with electrical maintenance, troubleshooting, or new installations, and you\u2019re tired of juggling different tools for secondary and auxiliary circuits, or you\u2019ve had a bad experience with testing tools that miss critical issues, let\u2019s chat. We can walk you through what our gear can do for your specific setup, whether you\u2019re dealing with small residential aux circuits or large industrial secondary and auxiliary systems. No hard sell, just real advice from guys who\u2019ve been in the field and in the workshop for years.<\/p>\n

Voltammetry Phase Meter<\/a> REFERENCES<\/p>\n

    \n
  1. Electrical Maintenance, Troubleshooting, and Testing: A Practical Guide, 3rd Edition, McGraw-Hill Education<\/li>\n
  2. Secondary Circuit Testing Best Practices for Industrial Systems, National Electrical Contractors Association (NECA) Technical Bulletin<\/li>\n
  3. Auxiliary Circuit Performance Under Load: Testing Methods and Failure Analysis, Institute of Electrical and Electronics Engineers (IEEE) Transactions on Industrial Applications<\/li>\n<\/ol>\n
    \n

    Wuhan Jiuhua Jingce Power Equipment Co., Ltd.<\/a>
    As one of the most experienced secondary circuit testing equipment manufacturers in China, we offer a wide range of products with superior quality. Please feel free to wholesale bulk durable secondary circuit testing equipment from our factory. For price consultation, contact us.
    Address: 601,Unit 1,Building D4-02,Optics Valley Center,303 OpticsValley Avenue,Wuhan
    E-mail: market@wuhanjhjc.com
    WebSite:     https:\/\/www.powertransformertester.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Hey everyone, let\u2019s cut to the chase because I get this question at least 3 times … Can secondary circuit testing equipment be used for testing auxiliary circuits in electrical devices?<\/span>Read more<\/a><\/p>\n","protected":false},"author":105,"featured_media":3585,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3548],"class_list":["post-3585","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-secondary-circuit-testing-equipment-4bed-311306"],"_links":{"self":[{"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/posts\/3585","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/users\/105"}],"replies":[{"embeddable":true,"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/comments?post=3585"}],"version-history":[{"count":0,"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/posts\/3585\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/posts\/3585"}],"wp:attachment":[{"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/media?parent=3585"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/categories?post=3585"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.peglersdesigns.com\/blog\/wp-json\/wp\/v2\/tags?post=3585"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}