AutomationDirect Logo Power Products Frequently Asked Questions

 

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Question: What is the difference between switching and linear power supplies?
Answer: The main difference is how they convert the AC line supply voltage to DC output volage. Switched-mode (switching) power supplies first rectify the AC line supply, and then transform it. Linear power supplies first transform the AC line supply, and then rectify it. Switching power supplies have better efficiency, less heat loss, wider input voltage ranges, smaller size and weight, and are intended for general use in automation. Linear power supplies have less harmonics, and (if regulated) have more precise output regulation.
FAQ ID: 853

Question: What is the difference between grounding and bonding?
Answer: Grounding is connecting your system to an earth ground. Bonding is connecting your system components to the grounding system. You cant have one without the other. If you do not have good bonding, then the chance of having poor low impedance pathways to ground will be present and will not allow for short circuit protection devices to function correctly. A poorly grounded system can also cause electrical noise to disrupt low voltage signals.
FAQ ID: 872

Question: What is a ground loop?
Answer: The ANSI/IEEE dictionary calls it "potentially detrimental loop formed when two or more points in an electrical system normally at ground potential are connected by a conducting path such that either points are not at the same ground potential." What does this mean It creates a pathway for current to flow. If one has a process control that works on a 4-20 ma signal, the added current from a ground loop could throw the reading off. This event can be catastrophic for some processes. The two main methods of elimination are: 1.) Eliminate ground loops (which may not be possible because some control and instrumentation equipment require ground as a reference.) 2.) Signal isolation. Each process or control system is different; its always a case-by-case basis if it will be affected by ground loops.
FAQ ID: 873

Question: Are there any standards for electrical installations?
Answer: The National Electrical Contractors Association (NECA) established the “Nation Electrical Installation Standards (NEIS).” You can find more information from http://www.necanet.org/ or http://www.neca-neis.org/
FAQ ID: 874

Question: Do the PS series power supplies have an isolated ground or is the negative leg of the output tied to ground either directly or indirectly by a passive or active component?
Answer: The output is isolated from the input and the -Vout is floating. The only connections to PE are the ones made by equipping the Y-Caps from Neutral to PE, Live to PE, -Vout to PE and +Vout to PE. These capacitors are used to meet the EMC emission standards.
FAQ ID: 939

Question: Do the PS-series power supplies have a voltage adjustment pot? If so, where is it located?
Answer: The PS-series have a small pot that is located approx. 0.5" under the grill frame of the units. There is no separate hole, you will need to look at the unit from the top to see it. It is located to the left of the DC output terminals.
FAQ ID: 1184

Question: Do you have SCCR (Short Circuit Current Rating) specifications for your power supplies?
Answer: According to UL508A Supplement SB Exception No 1, “Power transformers, reactors, current transformers, dry-type capacitors, resistors, varistors, and voltmeters are not required to have a short circuit current rating.” Power supplies are a type of power transformer and therefore do not require an SCCR rating.
FAQ ID: 1273