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Derating factors: the drum rating is not the rating in the tray

Type your own ordered list of sizes and base ratings, your own ambient, installation and grouping factors, and the load. The factors multiply, every rating on your list falls together, and the first entry that still covers the load is named, or nothing on the list does. Two more circuits bunched into the same tray can move that name with no line of the drawing changing. This page holds no table from any standard and it sizes nothing.

Live result

The first entry on your list that still covers 43.000 A is Size 16.
  • Your factors multiplied0.72
  • Rating after the factors43.200 A
  • Margin over the load0.200 A
Another loaded circuit or a warmer ambient moves which entry comes first.
The first entry on your list that still covers 43.000 A is Size 16.Another loaded circuit or a warmer ambient moves which entry comes first.

The ladder and the load line

The ladder and the load lineThe load is 43.000 amperes. Size 16 is the first entry that covers it at 43.200 amperes, leaving 0.200 amperes.

Your figures onlyThis page sizes nothing and is not a design. It multiplies the factors you typed and does nothing else. It holds no standard's tables, certifies nothing, and cannot see which factors apply to your installation.

Try a record

A

The load checked against your base ratings on the same basis.

4

This count reads the grouping factor you typed below.

0.90

Your factor, not one this page holds.

0.80

Your factor, not one this page holds.

Edit your list and exact factors

Your list of sizes

These three labels and their ratings are invented so the page has something to draw. Type your own over them. Ratings must rise strictly down the list. The order is your declaration, not something the page reads out of the names.

Entry 1
A
Entry 2
A
Entry 3
A

Additional factors

No additional factor is required.

Your grouping lookup

Three arithmetic shapes fill the twenty boxes before you type.

Exact factors

Every entry on your list

Size 10
Base rating
40.000 A
Resulting rating
28.800 A
Covers the load
no
Size 16
Base rating
60.000 A
Resulting rating
43.200 A
Covers the load
yes
Size 25
Base rating
90.000 A
Resulting rating
64.800 A
Covers the load
yes

The factors

Ambient factor
Value
0.900000
Installation factor
Value
0.800000
Grouping at 4 circuits
Value
1.000000
Combined factor
Value
0.72

Loaded circuits bunched together

circuits
circuits
circuits
circuits

It does not check the values in between.

How the answer sits across the values sampledA rail of the 20 values sampled, from 1 circuit to 20 circuits in steps of 1 circuit. Across the values sampled, the first entry on your list that still covers the load stays ⁦Size 16⁩ from 1 circuit, the lowest value sampled to 4 circuits. The nearest value where it changes is 5 circuits, where it becomes ⁦Size 25⁩.first change5 circuits4 circuitson the page

Across the values sampled, the first entry on your list that still covers the load stays Size 16 from 1 circuit, the lowest value sampled to 4 circuits. The nearest value where it changes is 5 circuits, where it becomes Size 25.

Across the values sampled, the first entry on your list that still covers the load stays ⁦Size 16⁩ from 1 circuit, the lowest value sampled to 4 circuits. The nearest value where it changes is 5 circuits, where it becomes ⁦Size 25⁩.
The answerSize 16
Values sampled1 circuit to 20 circuits, 20 values, step 1 circuit
Holds from1 circuit, lowest sampled
Holds to4 circuits
Nearest value that changes it5 circuits
The answer thereSize 25

What an unchanged region does and does not prove is set out in a short lesson.

Every admissible integer in this range was checked. Values outside the range remain unchecked.

Here is the maths

The formula, in words

Every factor you typed multiplies into one combined factor. Each base rating times that factor is its resulting rating. The page walks your list in the order you declared and names the first resulting rating at or above the load. Multiplication and the comparison use exact scaled integers, so displayed rounding never selects an entry.

A worked example

  1. F=0.900000×0.800000×1.000000=0.720000F = 0.900000 \times 0.800000 \times 1.000000 = 0.720000, where FF is the combined factor.
  2. I10=40.000×0.720000=28.800000I_{10} = 40.000 \times 0.720000 = 28.800000 A, below 43.000 A, where I10I_{10} is the rating for size 10.
  3. I16=60.000×0.720000=43.200000I_{16} = 60.000 \times 0.720000 = 43.200000 A, at or above 43.000 A, where I16I_{16} is the rating for size 16.
  4. I25=90.000×0.720000=64.800000I_{25} = 90.000 \times 0.720000 = 64.800000 A, where I25I_{25} is the rating for size 25.
  5. M=43.200000−43.000000=0.200000M = 43.200000 - 43.000000 = 0.200000 A, where MM is the margin.

Boundary

This page sizes nothing and is not a design. It multiplies the factors you typed and does nothing else. It holds no standard's tables, certifies nothing, and cannot see which factors apply to your installation.

Check it yourself

Set the circuit slider to 8 and then 9. The answer changes from Size 25 to Nothing on the list because your grouping value steps from 0.8 to 0.6 there. The step is in the table you typed, not in this page.

The calculation domain

The calculation accepts 1 to 50 sizes, ratings to three decimals, factors to six decimals and twenty grouping rows. This page offers 2 to 6 sizes so each row keeps a readable chart label.

Source anchor

IEC public scope page for IEC 60364-5-52. That published page describes a standards family concerned with selecting and erecting wiring systems.

Calculation version

1.0.0

The whole record prints. Your browser can save it as a PDF instead of printing it.

This page sizes nothing and is not a design. It will never supply a base rating, a factor, an installation method, a protective device, a conductor selection or a compliance conclusion. It describes what your typed list and your typed factors imply, and it does not determine whether any entry is suitable or safe.

Related

Rating record

Derating factors: the drum rating is not the rating in the tray

Accepted inputs

Load
43.000 A
Loaded circuits bunched together
4
Ambient factor
0.900000
Installation factor
0.800000
Entry 1 Label
Size 10
Entry 1 Base rating
40.000 A
Entry 2 Label
Size 16
Entry 2 Base rating
60.000 A
Entry 3 Label
Size 25
Entry 3 Base rating
90.000 A
Count 1
1.000000
Count 2
1.000000
Count 3
1.000000
Count 4
1.000000
Count 5
0.800000
Count 6
0.800000
Count 7
0.800000
Count 8
0.800000
Count 9
0.600000
Count 10
0.600000
Count 11
0.600000
Count 12
0.600000
Count 13
0.600000
Count 14
0.600000
Count 15
0.600000
Count 16
0.600000
Count 17
0.600000
Count 18
0.600000
Count 19
0.600000
Count 20
0.600000

All results

Tracked answer
Size 16
Load
43.000 A
Combined factor
0.72
Selected entry
Size 16
Base rating
60.000 A
Resulting rating
43.200 A
margin
0.200 A
Entry below
Size 10 28.800 A
Entry above
Size 25 64.800 A
Size 10
40.000 A, 28.800 A, no
Size 16
60.000 A, 43.200 A, yes
Size 25
90.000 A, 64.800 A, yes
Ambient factor
0.900000
Installation factor
0.800000
Grouping at 4 circuits
1.000000
Combined factor
0.72

Sweep of Loaded circuits bunched together

The assumption
Loaded circuits bunched together
Values sampled
1 to 20 circuits, 20 values, step 1
The answer
Size 16
Holds across
1 to 4 circuits
Nearest change
5 circuits, where it becomes Size 25
Reading the boundary
The sweep samples only the values you entered. Between samples the answer is not checked, so read the boundary as observed, not proven.

Record fields

Calculation version
1.0.0
Boundary
This page sizes nothing and is not a design. It multiplies the factors you typed and does nothing else. It holds no standard's tables, certifies nothing, and cannot see which factors apply to your installation.
Calculation trace
Multiply ambient, installation, grouping and every additional factor. Multiply each base rating by the combined factor. Walk the declared list in order and stop at the first result that covers the load.
Source anchor
IEC public scope page for IEC 60364-5-52

This page sizes nothing and is not a design. It will never supply a base rating, a factor, an installation method, a protective device, a conductor selection or a compliance conclusion. It describes what your typed list and your typed factors imply, and it does not determine whether any entry is suitable or safe.

Badr Alghamdi · badralghamdi.com/tools/rating-in-the-tray