Current draw for bench - Page 1
Forum section: electronics / beginners

author: bterrier
author_rank: Newbie
timestamp: July 31, 2018, 08:06:02 pm
content: Hello everyone,Planning to install some power outlets in the wall behind my workbench. I am wondering how much current a bench power supply and test equipment will require.I am running approximately 6 outlets on a dedicated 15amp circuit. Is 15a enough for the entire bench or should I upgrade to 20? I still have half a roll of 15a wire, so it would be nice to use it, but if necessary I will upgrade to the 20a wire, breaker, and outlets.Keep in mind, I am a beginner and hobbyist.Sent from my iPad using Tapatalk

author: nanofrog
author_rank: Super Contributor
timestamp: July 31, 2018, 08:22:34 pm
content: This will depend on what you'll end up running simultaneously (total current draw on a given circuit).For example in my case, the 120V circuits are 20A (old house, built in 1956). Granted, I've not tried to run every single item possible at the same time (no need to), I've never tripped the breaker.To put things into perspective, I've a window A/C unit that's always ON (say 10A IIRC as I live in a hot climate; i.e. 40C/104F these days) as well as all my computer stuff (likely another 2A or so). Yet despite all of this, running my oscilloscope, a couple of PSU's, and some other odds & ends, I still haven't managed to trip the breaker.So based on my experience, I wouldn't sweat it. Where this could be an issue, is if the circuit is shared by one or more current hogs (total sum is = or greater than 15A continuously).Hope this helps.BTW, if you go into your user profile and set your country, it's flag will be displayed beneath your userID. Makes it so much easier for other members to offer the most relevant information (i.e. pricing & availability; or in this case, mains voltage).

author: jpb
author_rank: Super Contributor
timestamp: July 31, 2018, 09:07:01 pm
content: As nanofrog has pointed out, current draw depends on the voltage. In the US or Japan current draw will be about double that in the UK or Europe for the same power.It also depends hugely on what equipment you use/can afford - ancient boat anchors have much higher power requirements than modern (but perhaps lower spec/ higher cost) kit. I've tended to restrict myself to more modern kit both for reasons of power and size but it does mean I've missed out on some ebay bargains.In my "lab" the highest current drawer is probably from linear power supplies which at say 30V 2A out probably draw 150W input. Otherwise it is my desktop workstation.For what its worth, I put my power requirements in this post:https://www.eevblog.com/forum/testgear/what-is-standardcommon-test-gear-dimensions/msg1599244/#msg1599244My summary is as follows:Current loading.Total wattage of current equipment (assuming power supplies are 40% efficient) is 1072W which would require everything to be on at once.13A at 240V is ~3kW.The workstation may be approximately 1 kW but can be plugged into a separate circuit.1072W at 240V is approximately 4.5A so power strips that go up to 10A should be fine.

author: james_s
author_rank: Super Contributor
timestamp: July 31, 2018, 09:45:13 pm
content: It will be different for everyone, but if I turn on every piece of equipment on my bench and run the power supplies at full load it adds up to less than 1kW, so it's no problem to plug everything into a single shared circuit. If you're doing high power stuff your situation would be different but most modern (as in less than ~40 years old) test equipment doesn't draw very much power.

author: ArthurDent
author_rank: Super Contributor
timestamp: August 01, 2018, 12:37:40 am
content: Having a dedicated run for your workbench does make it simpler. I rewired my old house with 12-2 with ground everywhere and the dedicated 120 volt run for the workbench has a high quality duplex 20A outlet with two 6 foot long industrial outlet strips with fuses, switch, protection, a lot of outlets, and a digital ammeter built into one end. I got these expensive outlet strips on Ebay for cheap because they weren't described that well and no one else bid on them. Some of the really cheap strips have outlets that will loosen up over time and may just use spring tension for ground contacts (not soldered) and can cause problems that are hard to pin down.Unlike the old tube-type frequency counter I had years ago that used neon bulb counting columns and ate up 600watt, My current counters (HP 53132A , Pendulum CNT-81) draw very modest power and most of the other equipment like GPS, frequency standards, DMM, scope, power supplies, etc., total 500-1000 watts if everything happened to be turned on and power supplies loaded.A 15A circuit would probably work just fine but if you only have 6 outlets I think you'll run out of outlets really fast and I would look into finding a good outlet strip or two with a total of around 24 outlets otherwise in the future you'll be adding computer style power strips to get what you need.

author: Brumby
author_rank: Unknown
timestamp: August 01, 2018, 01:04:49 am
content: Quote from: ArthurDent on August 01, 2018, 12:37:40 amThis was my very first reaction as well. The current capability wasn't going to be a big factor - unless, as said above, you are going to be running some higher power items. But those 6 outlets are going to get taken before you've put half your gear out. I'd put a power board on each of them.I also like master switches.

author: nanofrog
author_rank: Super Contributor
timestamp: August 01, 2018, 09:13:56 am
content: As mentioned, the # of outlets can definitely be an issue (certainly was in my case). Personally, I solved this with a 5' power strip (20 outlet) on the bench as well as some others elsewhere (UPS + an additional 8 ).No outlet in the house had a proper safety earth originally as this wasn't yet a requirement when the house was built. So I installed a 20AGCFIoutlet (aka RCD in other countries), drilled a hole through the wall for a ground wire that I attached to a ground rod I hammered into the earth.But as a home owner, I had such options that might not exist for others, renters in particular. So YMMV.

author: GreyWoolfe
author_rank: Unknown
timestamp: August 01, 2018, 04:03:18 pm
content: Quote from: nanofrog on August 01, 2018, 09:13:56 amI use an APC SmartUPS 1500 and I have 4, 8 outlet Belkin surge protectors attached on my workbench. I also have a desk for work and a desk for ham radio in my office plus an 8,000 BTU window AC as my office is an extension built on the house without air con ducts run to it. Interestingly enough, I just discovered that I have a lack of ground in the office so I will have to figure what outlet is on what circuit since I don't think all the outlets are on one circuit and figure out a grounding scheme.

author: drussell
author_rank: Super Contributor
timestamp: August 01, 2018, 04:55:20 pm
content: Quote from: GreyWoolfe on August 01, 2018, 04:03:18 pmMany commercial buildings rely on the conduit for ground on most outlets. Ones with isolated, separate grounds run to them are usually marked as such and colored orange.There is probably a bad connection at a conduit joint or a completely disconnected conduit joint upstream of the outlet(s) you're not seeing ground at. Often it is close to being right above where one of the outlets in the wall is when there is suspended ceiling. They sometimes get left in a poor state when people move walls, add a door, etc. in commercial space.If itissuspended ceiling, poke your head up there and see if you see any obvious lack of conduit. I often see things like open junction boxes with new feeds just Marretted into it without the conduits being physically attached or BX hanging there with power connected without the ground connected, etc. from where things have been (sloppily) moved around before. Often it is very easy to fix.