You need to power five new 3-phase machines in a workshop, 100 meters from the main switchroom.
The apprentice on your team sees two choices. Možnost A: Pull one “giant” 25mm steel-wire-armoured (SWA) cable to a new “Sub-Main” panel on the workshop wall. Možnost B: Pull five “medium-sized” 10mm cables—one “home run” for each machine.
The five smaller cables look cheaper on the invoice. So why do all the senior engineers insist on the “Sub-Main” plan?
It’s not a “style” choice. It’s the critical difference between “amateur” short-term thinking and “professional” system design. The “Sub-Main” wins on 4 critical points: Cost, Safety, Efficiency, and Future-Proofing.
Reason 1: The “False Economy” (Why 5 “Cheaper” Cables Cost More)
The first and most common trap is “The False Economy.”
- The “Amateur” Math (Near-Sighted):
(5 x 100m of 10mm cable) < (1 x 100m of 25mm cable) + (1x Sub-Panel)
Conclusion: The five cables are cheaper!
- The “Pro” Math (Far-Sighted):
You forgot the single biggest line item on any industrial job: Labor.
That “cheaper” plan requires:
- 5x cable trays or conduit runs.
- 5x cable pulls.
- 5x gland and termination kits.
- 5x separate tests.
- 5x valuable breaker slots in your main (and likely crowded) switchroom.
The “Sub-Main” (Option A) requires one of everything. One tray, one pull, one termination, one test.
Na stránkách Total Cost of Ownership (TCO)—materials plus labor—is almost always far lower for the single “python” cable. Don’t fall for “The False Economy.”
Reason 2: Safety & Maintenance (Avoiding “The 100-Meter Dash”)
This is the most important reason. It’s the one that separates a “safe” design from a “dangerous” one.
- The “Home Run” Nightmare (Option B):
A CNC mill faults, jamming a part. The operator hits the E-Stop. Now, your maintenance tech needs to perform Lock-Out Tag-Out (LOTO) before he can put his hands in the machine.
Where is the jistič?
It’s 100 meters away, in the main switchroom, hidden in a massive panel with 50 other identical breakers. Your tech has to take “The 100-Meter Dash,” pray the panel is labeled correctly, and then walk 100 meters back. It’s slow, frustrating, and a critical LOTO failure point.
- The “Sub-Main” Pro (Option A):
The machine faults. The tech turns to the VIOX Sub-Panel on the workshop wall, 5 meters away.
He opens the clearly-labeled door, flips the breaker for “CNC Mill 1,” and applies his LOTO lock.
He is “within line of sight” of his isolation point. He can vidět the panel while he works. This is the cornerstone of industrial safety.
PRO-TIP: “Local Isolation” is not a “nice-to-have”; it’s a fundamental safety requirement. A “home run” design (Option B) is a classic “amateur” design that creates an unmanageable and unsafe LOTO procedure.
Reason 3: Efficiency (The “Magic” of the Diversity Factor)
Here’s the “secret handshake” of electrical engineers. This is how the “Sub-Main” plan saves you even more money on the one “expensive” part: the giant cable.
- The “Amateur” Math:
I have 5 machines that peak at 20 Amps. (5 x 20A = 100A). I must need a 100A-rated “python” cable!
- The “Pro” Math (The “Aha!”):
What are the odds that all 5 machines will hit their absolute peak load at the exact same millisecond?
Zero.
When Machine A is at full-load cutting (20A), Machine B is idling (5A), and Machine C is off (0A). This is called “Diversity.”
Because of this, the Electrical “Regs” (like IEC 60364) allow you to apply a “Diversity Factor.” You don’t size the “python” for the 100A peak sum; you size it for the likely simultaneous load.
The “Magic”: You may only need an 80A or even 70A “python” cable to safely and compliantly power all 100A worth of machines. This “magic” only works with a Sub-Main design, and it saves you a fortune on copper.
Reason 4: Future-Proofing (The “30-Minute Upgrade”)
This is the final “pro” move: planning for the one thing that’s guaranteed to happen… change.
- The “Home Run” Nightmare (Option B):
One year later, the boss buys a 6th machine.
You groan. You now have to repeat the entire nightmare: find another spare breaker in the 100-meter-away main panel, order 100m of cable, and schedule a 2-day job to pull it.
- The “Sub-Main” Pro (Option A):
The boss buys a 6th machine.
You smile. You open the VIOX Sub-Panel (which you wisely ordered with a few “Spare Ways” / empty slots). You “click” in a new VIOX MCB.
You run a 5-meter “little snake” cable from the local panel to the new machine.
You’re done in 30 minutes. You’re a hero.
Conclusion: It’s Not “Style,” It’s “System Thinking”
That apprentice’s question had a simple answer:
The “5 Home Runs” (Option B) is “Short-Term Thinking.” It’s a “False Economy” that is more expensive in labor, less safe for maintenance, less efficient with power, and a nightmare to expand.
The “Sub-Main” (Option A) is “System Thinking.” It’s a professional infrastructure investment. It’s cheaper (TCO), safer (Local Isolation), smarter (Diversity), and flexible (Scalability).
Don’t fall for the “False Economy.” Be the “pro” who builds a system, not just a circuit.
VIOX’s complete range of configurable Sub-Distribution Boards, Enclosures, MCBs, and MCCBs are the tools you need to build that safe, scalable, and professional “System.” Browse our Sub-Main solutions today.
Technické Přesnost Poznámka
**Standards & Sources Referenced**
- This article is based on standard industrial electrical design philosophy.
- Concepts like "Total Cost of Ownership (TCO)" are standard business principles.
- "Local Isolation" is a core tenet of LOTO (Lock-Out Tag-Out) as defined by OSHA (US), HASAWA (UK), and equivalent bodies.
- "Diversity Factor" (or "Demand Factor") is a defined calculation in electrical regulations (e.g., IEC 60364, NEC Article 220).
**Timeliness Statement**
All technical principles and design practices referenced are accurate as of November 2025.
