{"id":351,"date":"2026-03-31T17:07:05","date_gmt":"2026-03-31T11:37:05","guid":{"rendered":"https:\/\/engcal.online\/blog\/?p=351"},"modified":"2026-03-31T17:07:05","modified_gmt":"2026-03-31T11:37:05","slug":"cable-size-20a-230v-50m-voltage-drop","status":"publish","type":"post","link":"https:\/\/engcal.online\/blog\/cable-size-20a-230v-50m-voltage-drop\/","title":{"rendered":"Cable Size for 20A 230V 50m: Wire Size Using 3% Voltage Drop (Example)"},"content":{"rendered":"

Cable Size for 20A 230V 50m: Wire Size Calculation Using 3% Voltage Drop (Worked Example)<\/strong><\/h2>\n

If you are searching for a cable size for 20A 230V 50m, you are already thinking like a practical engineer. You probably have a real circuit in mind, like a remote socket run, a small workshop feed, an outdoor supply, or a long branch circuit that needs to \u201cjust work\u201d without dim lights or nuisance issues. The reason this exact query is so common is simple. At 230 V, 20 A is not huge, but 50 m is long enough for voltage drop to become the deciding factor, even when the current rating is not.<\/p>\n

I have seen many installations where the cable \u201chandles the current,\u201d but the load still behaves poorly. Lights flicker. Motors run hot. Tools feel weak. Contactors chatter. These symptoms often get blamed on the appliance, but the real cause is the cable run. Voltage drop is quiet and sneaky. It usually does not trip a breaker. It just steals performance and reliability.<\/p>\n

In this guide, I will show you a clean, repeatable method to select a cable size for a 20 A, 230 V, 50 m run using a 3% voltage drop target. I will also do a full worked example with real numbers, then show you the practical checks that stop mistakes in the field.<\/p>\n

Why the 3% voltage drop target matters<\/strong><\/h2>\n

A 3% target is widely used as a good engineering rule of thumb for branch circuits that power sensitive loads, lighting, or general receptacles. Even when local standards allow a higher total drop across the whole feeder plus branch, aiming for 3% on a key run gives you margin. That margin becomes valuable when temperature rises, connections age, or load increases later.<\/p>\n

At 230 V<\/strong>, a 3%<\/strong> allowable drop is:<\/p>\n

3% of 230 V = 0.03 \u00d7 230 = 6.9 V<\/strong><\/p>\n

So if your source is 230 V, the load end should ideally stay above about 223 V<\/strong> under full load. That is the basic design target.<\/p>\n

If you allow 5%<\/strong> instead, the allowable drop becomes 11.5 V. That can change the cable size selection. But for many real circuits, 3% is the safer target, especially when the load is not purely resistive.<\/p>\n

The voltage drop basics you must get right<\/strong><\/h2>\n

Voltage drop in a cable happens because the conductor has impedance. In simple terms, it has resistance, and in AC systems, it also has reactance. Resistance usually dominates for smaller conductors and moderate lengths. Reactance becomes more noticeable as conductors get larger and runs get longer, or when the power factor is low.<\/p>\n

For a clean first-pass calculation on typical single-phase runs, you can model the drop using resistance only. That is the approach many quick calculators take, and it is often accurate enough to choose a practical cable size. You should still remember this is an estimate. Real installations add contact resistance, temperature effects, and sometimes meaningful reactance.<\/p>\n

The key point that many people miss is the return path<\/strong>.<\/p>\n

In a single-phase circuit, current flows out on the line conductor and returns on the neutral conductor. That means the \u201ceffective length\u201d for voltage drop is the loop length<\/strong>, not the one-way length. For a 50 m run, the current travels about 50 m out and 50 m back. So the loop length is 100 m<\/strong>.<\/p>\n

If you forget that, you can under-size the cable by one full size step, sometimes more.<\/p>\n

Step-by-step cable sizing method (the one I actually use)<\/strong><\/h2>\n

The workflow is simple if you follow it in the same order every time.<\/p>\n